If you don't have the PC version and have Xbox live, then Counterstrike is addictive as hell. The voice chat is hilarious. I'd like to strangle some of those little fuckers on there.
Don't get it though if you don't have Live or if you have access to the PC version.
The Suffering is good if you like single player games. The Chronicles of Riddick game was pretty amazing on the demo version too, almost Doom 3 quality graphics. Should be a good one to pick up.
This is actually a pretty reliable site for reviews:
http://www.metacritic.com/games/xbx/