I am a FPS guy. There aren't many Survival-Horror games for the 360 yet, but I am eagerly waiting for three releases -
Harker,
Left 4 Dead and
Resident Evil 5.
Among the FPS stuff, I would recommend :-
- Mass Effect - very engaging,
- Elder Scrolls IV: Oblivion - Arguably one of the best looking games ever made,
- Dead Rising - Awesome game, with some really neat levels.
Non-horror :-
Call of Duty 4, The Orange Box (a must buy) and
Assassin's Creed.