Rainbow Six: Vegas, looks awesome, same for F.E.A.R, they probably would be worth buying, I've heard a lot of good about them, I tried the demo of F.E.A.R. on my PC, but the performance was terrible, mind you I am below spec, but it was worth a try
The physics of it appear to be impressive and from what I've heard the overall gameplay is impressive, if you're PC is powerful enough for it, download a demo of both as they have PC versions and judge for yourself.
Prey is a game I would recommend, I've played it for PC as I don't have a 360, but it should be worth a purchase, I like it a lot myself, good graphics, good physics a good storyline to follow, good gameplay, good multiplayer. One feature I love is the fact that physics can changes, meaning you can walk up wall paths and walk along the ceiling etc. It's quite a peculiar game to play and is highly rated, I don't have the full version, but have played the demo that shows an awful lot, even two multiplayer levels.
"Listen to Jah Music..." - Bob Marley