I voted Civ4. My thoughts on the rest:
I voted nexus, my comments on your thoughts
Battlefield 2 -- Performance slug, too many bunny hopping / worm-dancing wankers, atrociously unfun if you play on a 'pub.' And of course, Fuck EA.
Pub play can be fun at times if you luck onto a good adhoc team. However at other times it can absolutely blow chunks. Also, ea's patches seem to have made things worse instead of better.
Darwinia -- Conceptually cool, but execution falls flat. It's Tron meets Sacrifice, except Tron 2.0 is a better at the setting and Sacrifice is better at the actual gameplay Darwinia's going for.
Its unique and cute, it feels more like a game from Nintendo seriously.
Nexus: The Jupiter Incident -- Heard bad things, didn't purchase. Been waiting for it to hit bargain bin price / get patched more.
You should try it, it is good. I didn't encounter bugs on my playthrough and the gameplay is challenging and well paced instead of being a clickfest. Also the storyline is pretty darned good too.
Rome: Total War - Barbarian Invasion -- Didn't purchase. Rome: Total War was boring enough.
Space Rangers 2 -- Interesting til you figured out how routine it all was. And of course, Fuck Starforce.
SWAT 4 -- I'm not a fan of tactical shooters, though it was apparently one of the better ones out there. Fuck their multplayer advertising scheme.
Didn't try this, was busy with DoD:S and BF2 at the time.
The Movies -- Fuck Molyneux.
Tried this, its the sims in hollywood. Unless you're into making movies in which case you can do all sorts of neat stuff, I lacked the paitence to get into the custom movies part so I let this game slide.
Tom Clancy's Splinter Cell: Chaos Theory -- Didn't play it; Fuck Starforce.
Warhammer 40,000: Dawn of War: Winter Assault -- Sweet expansion ruined by Relic's laziness in regards to patching/balancing. Imperial Guard were *way* overpowered at release (dunno if they still are). Campaign was boring. Broken Widescreen support. Buggy. Multiplayer notoriously unreliable, ie, Fuck Gamespy.
To be honest, I didn't find the guard that overpowered, but then again, I was only a fair to middling player to begin with. While not as good as the original campaign the new one had its moments. I didn't play in widescreen even on the original game (still using a 19" Trinitron). Didn't encounter bugs in skirmish/campaign... but I agree. Fuck Gamespy. The headaches I went through trying to host/join games were inexcusable.