Can you suggest some games for me to try for my xbox 360?

I’ve just gotten an xbox 360 and I already have a few games for it: Left 4 Dead 1 & 2, Bioshock 1 & 2, Blur and Mass Effect. I haven’t tried Mass Effect yet, but I plan on playing it today to see how I like it. I got it because it was highly suggested by multiple friends.

Except for a few games, my xbox-having friends seem to disagree on which games I should try, so I’m turning to fluther. What are some xbox games you fine people think I should try?