Rainbow Six Vegas is top notch and well rounded, great single player, great coop, great multiplayer. Best game on the system. Realistic isn't recommended if you suck.
Bioshock is polished in gameplay/story/presentation, haven't bothered to play more than a few hours though.
Oblivion was only fun when I decided to fill the leveling slots with abilities I wouldn't use, and played the game at level 1.
Gears of War was fun for a playthrough on the highest setting, and some coop, haven't touched it since.
Skate is a top notch skateboard sim with amazing graphics.
Dead Rising has great graphics and style. The boss battles were lame though and I never bothered to finish it. Had more fun when I said fuck the story and roamed around killing thousands of zombies.
Saints Row is good for a quick loadup to lay waste to the city, kill a few hundred cops/gang members, and then turn it off, like any GTA variation.
Medal of Honor Airborne is the best console ww2 shooter ever, bar none. Has a learning curve to it, I suggest starting on easy. You have to use the iron sights and aim for the head, puts them down in one shot and gives you lots of points to level up your weapons. Good graphics, good presentation, great gameplay. First fps I've played with a great cover system, iron sights, and A FUCKING SPRINT ABILITY. Fantastic game.
Dead or Alive 4 -- I hate fighting games, but I enjoy mashing through this. 60 fps and great AA is nice too.
Halo 3 -- yawn. Coming off of MOHA this feels so last gen. Halo 2.5.
Battlefield 2 - shit single player, fantastic multiplayer. Dedicated servers, decently balanced, and just really fucking fun.
xbla
Lumines, zuma, and geowars are awesome.
