After leaving meteor craters in the landscape of single and multi-player gaming with Half Life and Counter Strike, Valve has opted to take a pop at co-operative play with Left 4 Dead. The '4' in the title references the number of players you'll want to be involved at any one time, and that aspect of play really is the focus of the game. The premise is simple - you're stuck in a landscape overrun by zombies, and you and a small group of survivors need to stay alive. As a team, you'll need to make your way through four sprawling campaigns, keeping your buddies alive, if for no other reason than you want them to keep you alive for a few more precious minutes. To complement the co-op play there's a Versus mode that pits four survivors against four types of 'Boss Infected'. Each side presents a very different style of play, since the Boss Infected possess extra, double-hard zombie superpowers, such as the Smoker, which has a 50ft tongue that can drag survivors away from their group so, for example, and the Hunter can pin them down and pound the snot out of them. This all comes with a new kind of AI Valve has developed called the Director. This tailors the game to how you're playing in any given session. If you're lurking in one place, for example, it might unleash a fresh horde of the undead to hassle you. Conversely, if you're staggering around on the brink of death for a while, it might be kind enough to drop a health pack off in the next room. In any case, all that aside, gamers and lovers of all things zombie-related, form a line.