I've always thought the l4d community was pretty good. I think that's owed to the fact that winning requires a bit more teamwork than most other shooters. Yeah teamwork always makes it easier but it would be nigh impossible to win l4d if you did every man for himself, unless you moved fast enough to get to the end of the stage before everyone died. And I'm talking "You got caught by a smoker ? Yay that's a smoker not choking me !" style.