I haven't either but people talk like it is great.
I'll tell ya what though, I think Call of Duty 4 is just incredible. Unbelievable graphics. Now that orals are over, I can really dig in to that game. I also recently got Guitar Hero III. That is so unsophisticated compared to my other xbox360 games, but holy crap it is fun and addicting.
How about Gears of War? I haven't played it but heard is rather cool also. I like the "tears for fears" cover Mad World that is in the game though.