For 2009? There's literally nothing so far, and 2008 wasn't much better either. There's still five months to go this year, maybe one or two might be decent enough, but overall this year is mediocre if you compare it to 2000 to 2003 especially, with 2005 and 2007 being quite noteworthy as well.
Staring with 2008 and up to this day I would give honorable mentions to:
Fallout 3
Warhammer 40K: Soulstorm
Sins of a Solar Empire
Left 4 Dead
Dead Space
Red Alert 3
STALKER: Clear Sky
Red Faction: Guerrilla
Crysis Warhead
The "best" of that list would be Soulstorm and Fallout 3, for me, that is, of course this list is completely subjective, I know others will disagree, but it's my take on it. And note that I do not believe that any of them hold "best of the year" quality content, they're simply decent games with which you can have fun for some time, but going back and play them again constantly? Not really.