Lets see, well I currently own Perfect Dark zero(crap) Quake 4 good single crappy multiplayer, Kameo(delightfuly surprised by this game), D.O.A.4(if you like fighters get it), Ghost recon advanced warrior (pretty ok game), Call of Duty 2 ( best FPS game on the 360), Oblivion ( awsome rpg), Fight Night round 3 ( best looking on the 360, highly addictive),
Coming out july 11th chromehounds looks very promising.
October 2 Gears of War,sony fanboys will be kicking themselves in the nuts for not getting a 360.