How about the PC version of GTA IV? It's got Mods so that should give lasting appeal.
Saints Row 2 also had co-op which is nice for a game like that. I haven't played Fable 2 but people seem to say it lived up to expectations. Gears of War 2, and Resistance 2 seem to please the crowd as well, though I don't really care for either of them.
It's kinda tough thinking of games now that I'm trying to "review the year". I also like Clear Sky more than most people did but the popular opinion seems to be "not as good as original" though I disagree for the most part.
Time to meditate and think up a list.
(Oh yeah, I liked Dead Space too, nothing amazing but hey, threw it in there).
EDIT: WHen was the enhanced edition of The Witcher released? It's not a "new game" but it was one hell of an update and IMO should have honorable mention at least.