Left 4 Dead, out of the box - pretty cool. It's valve though so, I had high expectations. This is the first valve game I've picked up for my 360 instead of the PC, and I'm pretty impressed that even a thumb stick inept player like myself can pick it up.
Left 4 Dead is a zombie-survival-horror shoot 'em up. Light on the horror. It is very clearly designed to be played in a four (4 - see what they did there) person team. A note to all zombie watchers, these are your new fast zombies not your classic shuffling zombies.
I've played through the first two "movies" with friends online. I like that the campaigns, of which there are 4 classic zombie movie scenarios, play out in well organized, check pointed chunks. The graphics are acceptable to good.
I would like to be able to share more, but my 360 has decided to join so many of it's brethren and display me 3 red lights instead of zombie game goodness. It's on its way to Microsoft now. And I was just getting my Rock Band 2 practice routine down.