Recently I've been replaying Supreme Commander Forged Alliance, skirmish and replaying SP campaign on Hard.More detailed gameplay information (or a review of sorts) moved under spoiler.
WARNING: WALL OF TEXT HEAVY.
Supreme Commander is an RTS and Forged Alliance is a standalone expansion pack for it.
The most notable thing of SupCom is Strategic View. You can zoom the main view out to observe the entire map, and then zoom in to see the smug face of your Armored Command Unit.
Full zoom-out. An entire map is observed.
Build system
SupCom is considered to be a Spiritual Successor of sorts to Total Annihilation and utilizes similar build system: at the start, you get an ACU, Armored Command Unit. It can construct (3D-print, basically) some T1 buildings, such as factories (Land, Air, Naval), mass extractors (built only on mass deposits) and power generators. To assist ACU in base building or expansion, any factory can build Engineers, amphibious vehicles that can construct buildings of its tech level. In addition, support ACUs can be summoned via T3 Quantum Gate. Builders can also assist buildings (or other units, e.g. T3 Strategic Missile Sub or T3 Carrier) in building or upgrading.
Tech levels
Three of them, T1, T2 and T3. Experimentals are sort of their own level, but can be built by any T3 builder. Factories can be upgraded to the next level, ACU can be upgraded to construct T2 and later T3 buildings via customization tab.
Intelligence systems
Units' vision range is smaller than their fire range in nearly all causes, especially in the case of artillery and anti-air. However, the visual detection isn't the only way to spot the target - in most cases they will fire at radar blips. Radar and sonar detection is provided by special structures and some units (T1 Scout, T1 Frigate and T1 Air Scout, for example). There are ways to counter it - jamming creates fake radar blips and stealth (personal or field) hides units from radar. The optical cloaking is also present. These electronic warfare measures, however, are likewise countered by Omni Sensors, provided by T3 radar station.
Radar can tell apart buildings from units, but will determine unit's type based on terrain. For example, it will determine Salem class destroyer walking on land as a land unit. SupCom also "remembers" location of buildings even if you lose radar/optical sight to them.
Units
Come in various flavors: land units, planes, low-flying aircraft (gunships and transports, essentially helicopters), surface ships and submarines. Submarines are safe from most surface weapons, so are planes and gunships. Gunships usually can engage each other.
Aircraft are notable in that they have a fuel meter. If it runs out the aircraft will notably slow down. If it's on patrol it will automatically head off to land on nearest free airpad (available as T2 building for all four factions; can also be provided by units such as Cybran T2 Cruiser). Airpads swiftly refuel and repair planes landing on them.
Transports can move only land units and (s)ACUs. They can be set to assist the factory; they will carry produced units to factory's rally point. Also transports can be set up to ferry units, useful for relocating a group of units in more than one run.
Experimental units are your Wonder Weapons. They are expensive, but very powerful, and some of them are game-enders of sorts.
Weapon systems
Some nuances are here too. For example, torpedoes can't be used against hover units but are only thing that can hit submarines. Direct fire guns can be messed up by line of fire obstruction. Tactical missiles can be intercepted by tactical missile defense buildings or units (such as T2 Cruiser). Anti-air can be provided by light AA guns, area-of-effect flak cannons or tracking and homing SAMs. Damage can be stopped by shield dome generators, which will be handy to defend a base from T3 Heavy Artillery (VERY long range, think WWI era Paris guns and you won't be far off).
Nukes don't care about shields. But they are manually built, take lots of resources and time, and can be stopped by strategic missile defense. But if they land they can be quite powerful, and they are properly announced. STRATEGIC LAUNCH DETECTED.
(And technically only UEF Strategic Missiles are nuclear weapons. Other factions have other types of devices. Ironically, the nukes don't have EMP effect while Cybran Strategic Missiles do. In Supreme Commander 2, all human factions switch back to nukes and this time they have the EMP.)
Economy
Two types of resources are used, Mass and Energy. Mass is typically used for construction, Energy - also for various other needs such as radar, counter-intelligence, shields, artillery reloading, etc. The game has a real-time economy system.
Also the game has an adjacency bonus: building resource-producing buildings next to resource-consuming one will decrease the consumption of that resource (e.g. surrounding a Mass Fabricator or a Shield Generator with Power Generators will decrease their energy drain), while building a resource-storing building next to resource-producing one will increase the income (e.g. surrounding a Mass Extractor with Mass Storages).
(While this is effective, Power generators can explode upon destruction, so it's risky to some degree).
Factions
I think Mike has stack buffer overflow at this point.
UEF
Or United Earth Federation. No-frills Powerhouse faction. Great direct-fire guns and artillery, good armor, average shields. Proud owners of T3 Point Defense emplacements and T2 shield boats as well as the longest ranged T3 battleship. However they lack a T3 Carrier.
Notable units:
Titan T3 Siege Assault Bot: Relatively fast walkers with a pair of decent guns and pair of tactical missile launchers (removed after patch). Titan is equipped with a personal shield, making it capable of surviving ACU explosions.
Percival T3 Armored Assault Bot: Slower walker with a single cannon. It has slow rate of fire, but long range. It can also walk on the sea bottom.
Broadsword T3 Gunship: First T3 Gunship in SupCom (Cybran and Aeon equivalents appeared only in FA). Armed with an AA railgun and a plasma cannon from Titan.
Ambassador T3 Strategic Bomber: This thing looks like a B1 Lancer and drops tiny nukes, also has a dinky tail railgun.
Governor Class T2 Cruiser: As all cruisers, Governor class is a fragile vessel armed with anti-aircraft weapons, tactical missile defense and dinky gun. Like Seraphim T2 cruiser it's also armed with tactical missile launcher.
Summit Class T3 Battleship: Armed with three three-barreled Gauss Cannons, two AA railguns and tactical missile defense. Longest main cannon range among battleships.
Experimentals:
-Fatboy Experimental Mobile Factory: THE Military Mashup Machine, this is a factory on threads with some machine guns and four turrets from Summit Class, shield dome, basic AA, torps (for when it gets underwater) and airpad. Not much in terms of resilience, though, and a fair bit of its hitpoints are in its shield dome, but can produce serious bombardment alone, not mentioning any friends it can pump out (and it might be anything UEF T3 Land Factory can create, you might want to start with a few T3 Engineers to assist it).
-Atlantis Experimental Submersible Carrier: IJN I-400 on crack. A submersible carrier with SAMs to use from surface and torps. Being a carrier it can build and store aircraft, such as T3 Stratobombers. Pretty cheap too.
-Mavor Experimental Artillery Installation: Paris Gun on crack. An artillery gun with unlimited range. And quite accurate at that.
-Novax Center Experimental Satellite Uplink: A control center for a Kill Sat that can pwn stuff from above safe from retaliation as long as center isn't destroyed. If it is the sat goes down.
Cybran Nation
Cheesy gimmicks, cheesy gimmicks everywhere! Enjoy moar dakka and like fast units, maybe that's why they prefer red. However that's where their Orkiness ends - the Cybran Nation is Subversive to no end. They don't tend to hit that hard, their artillery is inaccurate (but with bigger AoE), their shields are weakest and they lack mobile shields. However, they have a lot of radar stealth - they have mobile stealth field and Mermaid class counter-intelligence boats, not to mention personal stealth on their T3 fighters and bombers. The stuff of nightmares, however, is stealthed, cloaked Cybran ACU with a HEAVY MICROWAVE LASER. Aside from that, Cybrans tend to put non-stealthy gimmicks on their units too, with most EMP effects (the largest example is EMP Flux Warhead, their nuke equivalent) and side abilities.
Notable units:
Loyalist T3 Siege Assault Bot: Relatively fast combat walker with two different weapons (low-RoF high-damage and weak fast-firing one). Obligatory gimmick is tactical redirection which sends tactical missiles back to sender; this is why you don't use UEF ACU's backpack tac nuke against Cybran. Since Tac Redirection doesn't destroy the missile, it is ironically effective against Cybran splitting tactical missiles. Upon destruction Loyalist EMPs all enemy units in a small radius around it.
Brick T3 Armored Assault Bot: This unit is slower, has a high-RoF moderate damage gun. Like Percival it can walk under water and is even armed with weak torpedoes for self-defense.
Gemini T3 Air Superiority Fighter - Decent ASF, Gemini is armed with very accurate AA missiles and equipped with Radar Stealth.
Revenant T3 Strategic Bomber - Drops relatively low-damaging bombs with large AoE. Like Gemini, Revenant is equipped with personal Radar Stealth generator, but has less HP to compensate.
Wailer T3 Heavy Gunship - Cybrans' answer to the Broadsword, Wailer carries AA missiles, decent gun and radar jammer. Best used in combination with Renegade T2 gunships that have AoE attack.
Salem Class T2 Destroyer: A ship dedicated for anti-ship combat. Salem Class Destroyers are armed with a long-ranged and high-RoF cannon, weak AA autocannon, torpedoes and torpedo defense. However, this ship also has one unique feature: it can deploy legs to walk on land! While it moves very slowly while on land, it offers decent firepower.
Siren Class T2 Cruiser: Classic T2 Cruiser package of good AA and TMD on a fragile hull. Except, Siren also carries a decent cannon and can switch its AA weapon to engage land targets, albeit it's very inaccurate in anti-ground mode, feature shared with Sky Slammer T1 Mobile Anti Air. Ships are bigger targets and shield domes are even bigger so there's that.
Galaxy Class T3 Battleship: Armed with a decent sixpack of cannons, two weak AA autocannon, two tactical missile defense cannons and decent torpedoes, Galaxy Class Battleship is decent in fleet engagements, mainly thanks to torps.
Plan B T3 Strategic Missile Sub: Like all T3 SMS, Plan B is armed with tactical missiles and can build and launch strategic missiles. Unlike them, Plan B is also armed with decent torpedoes and poses a threat to enemy ships even without using tactical missiles. In addition, all Cybran tactical missiles (Viper T2 Mobile Missile Launcher, TML-4 stationary missile launcher, Plan B) split into submunitions when hit by Tactical Missile Defense.
Experimentals.
-Monkeylord Experimental Spiderbot - A cheapest experimental, that doesn't stop this spider-like six-legged walker from eating entire low-level armies with its heavy microwave lazzor or just crushing them. Lazzor has the highest DPS in the game and can be rotated 360 degrees. Monkeylord is relatively maneuverable and fast (for an experimental unit) and easier to mass produce, but less resilient; gunship swarms and stratobombers will dismember it in no time. Also has a couple of longer-ranged guns, some SAMs, shitty torps and radar stealth.
Five Cybran Monkeylords in combat. Three of them are firing Heavy Microwave Lasers.
-Megalith Experimental Megabot - Bigger, four-legged walker armed with two pairs of giant guns, single flak cannon, more or less good torps and ability to build some units (T2 Mobile AA, T3 Engineer, T3 Armored Assault Bot, T3 Mobile Artillery). Megalith has no support guns with a high rate of fire, so it will most likely need support, which can be provided by Monkeylords (which provide close fire support with their lasers and cover from air) or Bricks (which Megalith can build). Aircraft are also a threat, a bit offset since it can build T2 Mobile Flak Artillery. Good torps and high vantage point of cannons make it a good sea experimental.
-Soul Ripper Experimental Gunship - A giant flying bug with tons of guns and rockets, plus some AA missiles. Quite slow though, but can eat hordes of non-experimental land units. However a horde of T3 fighters will murder a Soul Ripper easily.
-Scathis Experimental Mobile Rapid Fire Artillery - Basically self-propelled gatling artillery with a murderous rate of fire. Only land-based non-amphibious experimental, but it matters little since FA made its range unlimited (in MP and skirmish but not in campaign), rendering its entire "self-propelled" shtick pretty moot (unless your opponent is well on the whole "counterbattery fire" thing and relocating the thing after few shots to avoid retaliation is actually viable). Eats lots of energy though (10k per shot), and wildly inaccurate (well, as all Cybran artillery is). The downside is... it's not a building and will not benefit from Adjacency Bonus, meaning no way to reduce its monstrous power hunger/further increase its murderous rate of fire.
Aeon Illuminate
The Glass Cannons. They hit hard and fast, but aren't best at taking it back. Lots of hover units. Also tend to keep minimalistic loadout of units, nearly no gimmicks in contrast with Cybran. Also they have five experimentals in FA, but one of them is misclassified as T3 - the Heavy Rapid-Fire Artillery. Nonetheless that thing costs more than some experimentals. Quite a lot of their usual units are also powerful. Notable Units:
Aurora T1 Light Tank: Aeon T1 tank is the key component to Aeon Zerg Rush thanks to their powerful cannons and hover propulsion.
Harbinger MkV T3 Siege Assault Bot: Aeon equivalent to Titan and Loyalist, Harbinger is protected with a tiny shield bubble. It can repair other units and reclaim wreckages.
Sprite Striker T3 Sniper Bot: Carries a long-ranged direct-fire weapon. Must remain stationary to fire and is fragile.
Restorer T3 AA Gunship: Whooo boy, where to START? It's armed just as good as Aeon T2 gunship, beefier, has AA missiles and is DIRT CHEAP compared to other T3 gunships. Some claim the worst thing that happened to SupCom was Restorer Spam.
Solace T3 Torpedo Bomber: Bane of battleships and most ships overall.
Omen Class T3 Battleship: Three Oblivion cannons and TMD. Nothing more, Aeon style. The shortest range among battleships.
Torrent Class T3 Missile Ship: Compensates for Omen Class short range, Torrent launches massive salvos of tactical missiles.
Experimentals
-Galactic Colossus Experimental Sacred Assault Bot - a giant (like, really giant, it dwarfs ACUs) mecha with a huge eye laser (less DPS than Heavy Microwave Laser for some reason), two tractor claws (drag units closer and instakill them - beware of Loyalists' death EMP!) and 99999 HP. And that's all. No AA, no torps or anti-torpedo defense, can't hit targets behind it, but it will facetank ten shitloads of firepower before hitting the dirt. How many damage will it cause before that happens is up to how you support it. Oh, and it also has Omni Sensor, Cybran S&C commanders beware.
-Czar Experimental Flying Fortress - a flying saucer a la Independence Day. Aside from giant laser in the bottom has AA missiles, flak cannons, depth charges. It is also a carrier, so it can also pump out ten shitloads of T3 AA Gunships. If it goes down nearly anything under it is flakked.
-Tempest Experimental Submersible Battleship - Another saucer, this time seaborne. Has lots of torps, a giant cannon and can build T1-T2 ships and T3 Engies.
-Paragon Experimental Resource Generator - A building that can ensure you'll always have enough mass and energy. Literally, forget about economy, you have all the resources, ALL OF THEM. However, when it goes down, it goes out with a bang equal to that of a nuke, and it's not that resilient. Are ya feelin' lucky?
Seraphim
These guys are aliens and it shows. They don't have SAMs (use fast-tracking long-ranged guns instead, T2 Cruiser also has flak cannons), rolled T1 Scout and T1 Light Assault Bot into one unit, lack T3 Missile Sub (T3 Battleship builds/launches nukes and T3 carrier has tactical missiles), their T2 Destroyers can submerge... Similarly to Aeon, they have lots of hover units. They are gimmicky, but not much, so they appear to be Balanced between the three factions. Also, best shields in the game.
Notable units:
(Note the weird names. Actually, those are apparently just descriptions in Seraphim language. E.g. Seraphim Engineers are called Iya-Istle, Iya and Iyathuum => "lesser builder", "builder" and "greater builder".)
Ilshavoh T2 Assault Bot ('-shavoh' apparently stands for "anti-" prefix) - Seraphim equivalent to MBT, Ilshavohs are faster and decently powerful, so they can remain viable even after T3 jump, just in much bigger numbers.
Othuum T3 Siege Tank - Equivalent to Siege Assault Bots, Othuums are slow, can traverse sea bottom, armed with a bunch of guns and torps. They are slower, but good as fire support.
Usha-Ah T3 Sniper Bot - A long ranged glass cannon like Sprite Striker, can sacrifice speed and reload time for more power.
Uashavoh ("ua-" apparently means "naval", so "anti-naval") T2 Destroyer - Aforementioned submersible destroyer. On surface also armed with two beam weapons.
Italua T2 Cruiser - AA&TMD vessel (aka Cruiser job description), carries no direct-fire weapons, but has tactical missiles.
Hauthuum ("hau" = "ship", so "greater ship") T3 Battleship - typical shore bombardment vessel with extra AA guns and TMD, except it also has a nuclear missile silo to compensate for the lack of T3 Strategic Missile Sub.
Iavish ("ia" = "aircraft", "vish" = "carrier" => "aircraft carrier") T3 Carrier - Admiral Kuznetzov on alien steroids. Like all other carriers, has a set of AA weapons and can build and store aircraft. Seraphim carrier also has a tactical missile launcher also to compensate for the lack of T3 SMS.
Yathsou ("sou" = "submarine") T3 Submarine Hunter - A sub with powerful torps, bane of all battleships that aren't Galaxy class (and even then it's gonna get pretty hurt). Also has an AA autocannon for use when surfaced.
Experimentals:
-Ythotha Experimental Assault Bot: Exp. Assault Bot - A giant walker similar to Colossus. Less HP, but more guns, some of which are AA. Upon destruction releases some uncontrollable entity that attacks random places for some time, then expires.
-Ahwassa Exp. Bomber - A giant plane that drops a high-yield bomb, also has some AA. It takes a long bombing run, but it has decent amount of HP and its bombs eat bases. Forged Alliance Missions 4 and 6 can be easily passed by stealing a Seraphim engineer and building a metric flak ton of these babies. Bonus irony points since apparently, Seraphim used these in their opening alpha strike on Earth. Also, it's friggin beautiful.
-Yolona Oss Exp. Strategic Missile Launcher - A giant missile silo that launches a giant strategic missile. Said SM has bigger AoE and damage and takes two SMD hits to stop.
Singleplayer Campaign
Original Supreme Commander has three campaigns, one for each side, all of them revolve around UEF superweapon called Black Sun, with which UEF hopes to turn the tide in the Infinite War. Meanwhile two other factions want to use the Black Sun for their own purposes. UEF is apparently losing the war, Cybran Nation is flakked if UEF loses but they have the plan, and Aeon Illuminate is apparently winning but there are inner tensions between their leader and supreme commander, which results in Aeon civil war.
Regardless of what faction you play as, the Black Sun fires. It results in Quantum Rift which Seraphim uses to invade our galaxy, and everything goes straight to hell. Part of Aeon Illuminate and Cybran Quantum AI (as well as Seventh Hand Node) turn against humanity while acting leaders of UEF and Aeon together with the leader of Cybran Nation form the alliance to save humanity's collective asses.
Forged Alliance has one campaign for three original factions (you can still play as Seraphim in skirmishes and MP). There are still differences in dialogue lines and secondary objectives depending on the faction you play as. However if you want to play one mission after the first as one faction, you need to complete previous mission for that faction.
Some missions are easier for certain faction. For example, Mission 4 is easier for UEF players with their Ravager T3 point defense turrets, while Cybran are going to spam Soulrippers and Monkeylords and hope for the best. Also in Mission 4 you can steal a Seraphim Engineer and spam the flak out of Ahwassas in order to go on the offensive. Mission 5 is just cool when playing as UEF because secondary objective gives you an Aeon sACU and you can steal a Cybran Engineer, giving you the tech of three factions! And Mission 6 gives you an UEF and Aeon sACUs, which means that if you play as Cybran and jack a Seraphim Engineer, you will have access to tech of all four factions. I managed to do that, and flak if it wasn't fun to have a giant pack of Ahwassas bombing everything to the stone age.