Soldato
Spore
Most disappointing game has to be Far Cry 2. I did the first few missions, almost died of boredom, then sold it on.
In fact, I think it's been a fairly poor year in general. Tomb Raider: Underworld was a bit naff compared to the last two, and Fallout 3 had a lot of potential but for me fell very short.
Mass Effect was good, but could have been so much better had they not just copied and pasted the same planet 20 times and left them bereft of anything to do on them. The first planet was great, and had me thinking this could be the next KOTOR, but it wasn't to be.
The better titles this year for me have been Prince of Persia (finally found all the crystals) and the suprisingly brilliant Dead Space.
In the casual section, World of Goo was pretty good.
Not sure I really have one at the moment, GTA4 I guess, I kind of got caught up in the hype but after playing it for a day or so just lost interest...
Farcry 2 by a huge amount