Left 4 Dead, the name is in the title.
I wasn't gonna get it, but since the demo is this: Uber, I pre ordered it. It is out on the 18th of November, I think.
Have to use Steam to get it. You have Steam, right? If not, how the hell have you been playing Portal?
You don't want to know what I'll do to you if I discover you haven't been playing Portal.