I bought it on PC. The matchmaking leaves a lot to be desired but the game is certainly not empty. It tends to match you with games that only have 1-2 other people in it, but I always abort that and try again. It rarely takes me more than 4-5 minutes to get a game going with 4 people in it.
That said the game isn't breaking any new ground. It's fun and I'll get my money's worth out of it, but L4D it ain't. There's nothing here we haven't seen before, but if you need your fix of shooting swarms of zombies in the face, it hits the spot.