Most of you may already know this, but for the newcomers, here's a little primer on Left 4 Dead. You play online with 3 other people in various co-op campaigns, each lasting around an hour. These campaigns consist of various movie inspired setpieces and have all four of you survivors trying to reach the end of the level where an escape vehicle will come for your salvation. On the way to the extraction point, you fight various mini-bosses, with the finale (waiting for the rescue vehicle) being the part where all hell breaks loose. Oh, and you kill zombies, lots and lots of zombies.