I might try Left 4 Dead. I didn't care for it too much when I played the demo, but the demos aren't always very telling. I got a year Live subscription for Christmas so I might check it out if the multiplayer is good.
i have left4dead yet i havnt played it yet funny enough. ive heard that its similar to the demo. play the game on expert or the 2nd hardest with a good group and u'll have a blast man