Aside from Silent Hunter III I've been overtaken by the sudden urge to replay Starcraft II trilogy.
Starting from Wings of Liberty, and even then I started from the middle using my old saves. Alas I missed out the cool missions: Redstone III (Reaper hit-n-runs) and Xil (SIEGE TANKS).
Replayed the side storyline with Zeratul's crystal, due to all the research points I would get from it. Except that I used instant win code in the last one, but at that point the objective was "hold the line to the last protoss" but between a flak ton of Carriers and ranks of Photon Cannons I could hold the line painfully long. Were Protoss trying to one-up Terrans? 'cos I'm sure that in the same situations, Siege Tanks, cruisers and bunkered infantry could hold the line much better.
On that note, research and upgrades proved actually useful. Little tweaks to usual units, and research can unlock new ones (those are not subject to upgrades, pity).
The really cool parts are that you can meet old units from Starcraft I/Brood War. Firebat, Medic, Wraith, Goliath, Science Vessel, Vultures, etc. Some are situational, some are awesome, some are decent. Science Vessel is particularly cool; it can repair your stuff and irradiate enemies. For example, in the Char Infested Platform Science Vessels killed the Zerg Leviathan by Irradiate kiting.
Of course, some old units are too symbolic to get rid of them. Marines remain ever useful with their numbers and ranged attack. Siege Tanks' powerful AoE ranged attack in Siege Mode is also valuable in Hold The Line missions as well as in their intended purpose of waging a siege, and their new model - especially the model of a Mercenary Siege Tank - is just beautiful. Battlecruisers, well, they changed, they have a flak ton of weaker attacks instead of a single powerful one, they still have Yamato Guns though. However now they can get Defensive Matrix (a temporary shield) and Missile Batteries (AoE AA attack). Ghosts... I opted out of using them, and they lost Lockdown anyway so... meh. I took Spectres instead, because a) they have essentially a handheld Yamato Gun; b) I don't like that blonde Kerrigan clone you have to help to get Ghosts. And I used them, like, in one mission.
New units are also mostly cool. I especially like Marauders (slowdown grenades are good value), Banshees (Stealthy death from above, combo well with Wraiths), Thors (Heavy assault unit with AA, 330mm Cannons and Immortality Protocol are just the icing on the cake), Diamondbacks (fast, powerful and can fire on the move) and Hercules Transports (large, resilient spaceships that can carry a sh*t ton of units in one go, three Thors for example, and nearly instantly deploy them, if it goes down its passengers use escape pods). Vikings are also useful, especially since you can apply AoE effect to its AA missiles (Anyone remembers UED Valkyries?) and they have longer range than Wraiths, but Viks can't cloak and have to transform to attack ground targets.
As for the story... Missions are fun, most of them. The secret mission in particular. I played through all the main storyline quests until Quadrant Sigma, then completed Tosh's sidequests and then Hanson's. The Zombie Apocalypse mission is easier when you have Siege Tanks, Banshees and permacloaked Spectres. If the infected have detectors/point defense, just nuke them!
Finally, Char missions. I went for denying the Zerg air support so I'll be able to irradiate Leviathan to death. Nydus Worms in the last mission can be hunted down with Banshees. Hive Mind Emulator was invaluable - jack an Ultralisk, watch the shredded zerglings fly. The idea was to also build some Planetary Fortresses on the frontlines.
The storyline itself, however, is not without flaws. If Raynor has been doing nothing but getting hammered for 4 years, he shouldn't be able to lead his ass out of a paper bag, much less a rebellion. No wonder Kerrigan had to actually do the rebellion for him. But oh well, he snapped out of this and started gettin' stuff done. Aside from that, it was a fun ride. I first played WoL when I was in 8th/9th grade and I still find it enjoyable. Especially when it comes to Swann, Tychus or Raynor cracking jokes, Raynor's humor in particular keeps the character from becoming boring.
Finally, Hyperion's interface is nicer than that of the Leviathan or Spear of Adun. There's a jukebox and a game console (and a holostripper, but I like to pretend I didn't notice it) in the cantina, you can get a close-up looks at some particularly cool units in the Armory (Yes, they have a SIEGE TANK in there, and yes, it plays its deploy animation).
I'll post my thoughts on Heart of the Swarm in a later post after I'll complete its campaign.