It would be another Left4Dead scenario as downloadable content on Xbox Live (as an exclusive, too, just because it would make PS3 owners mad. )
I want to support everything that Curtis said about the game in the previous post. Though I must admit that I am quite bad at the game. Curtis, if it makes you feel any better, I'm trying to improve my skills. I'm just a squirrel, trying to get a nut, dogg.
This game has no virtually no exposition save a short cinematic at the beginning, yet it is ridiculously replayable, in part, because the experience seems strangely authentic - though at first I thought the opposite. I must compare every shooter to Quake and Goldeneye, and this game is not like either of those. Obviously Valve's Source engine makes things smooth and buttery, but the real fun is in the cinematic way the game plays out; how music cues actually create tension, react to the gameplay, and warn the player; the interaction with your teammates; the randomized spawn points for items and zombies.
The special infected are a special treat, especially the Tank. I like to pound the shit out of the survivors. This is in another mode, naturally, where you get to play as the infected and terrorize a team of real human opponents. The graphics are hot, as is the norm for Valve, and the gameplay is crisp. I suppose one could make small criticisms about the lack of scenarios (there are only four, but the random nature of the game allows for any number of replays, depending on how much fun you have killing zombies with shotguns; here's a hint - it's really fun), or the sometimes tedious task of avoiding friendly fire, but overall these complaints barely detract from the overall gameplay experience, which is actually the reason we play games. Or that's the reason why I think we play games.
Playlist:Left4Dead; Oblivion (how did that happen again!??); Gears of War 2; Rock Band 2