I loved Left 4 Dead 2 on the 360.
A lot of people cited the Assassins Creed series. I tried 1 and didn't like it. I later picked up 2 and found it much better, but kind of burned out on it about 2/3's through it. In the middle if 2, I picked up 3, but never started it because I have to finish 2.
I think I'll give it another shot.