Halo 3. Lots of games are as much fun but none of them are supported aswell by the developer and have as much longevity.

I cant decide. depends on the Genre

TPS = Gears 1
FPS = Halo 3
Racing = Forza 2
RPG = Mass Effect
RTS/Strategy =Halo Wars
Music/Rythem = Rock Band 2

Probably my favs are Mass Effect, Halo 3, Gears and Halo Wars

Bioshock was amazing to me, that would be my #1.
Mass Effect and Fallout are right behind it though.

First place goes to Mass Effect, but Halo 3 is a close second just because of the longevity of the game and how fun it is to play.

1st: Bioshock
2nd: Mass Effect
3rd: Fallout 3


Good games these are.

1. Halo 3
2. Ninja Gaiden II
3. GoW 2
4. Halo Wars (might change haven't finished the game)
5. Mass Effect

btw looking at that list really does show the variety of high quality titles the 360 has :)

i love fable 2. its still my favorite game so far. however my sister tells me that RE5 is better. the funny thing is i reserved it months ago and haven't played it once. it seems lately i've been hooked on my psp :)

Dead Rising and Tales of Vesperia.

Left 4 Dead

you can't stop the zombie apocalypse :p

There are a few that come to mind but don't quite make the cut (Lost Odyssey, Gears of War 2), but overall I'd say GTA4 and Street Fighter 4 (GTA for singleplayer, SF4 for multiplayer)