"Close the god damn door!" shouts a character from Valve's four player co-op zombie shooter Left 4 Dead. Frantically the players scramble towards a safe house before it's too late and they are overrun by the zombie horde. As the last player gets inside his team mate closes the door as the line of zombies behind him slam into it snarling. At this year's Penny-Arcade Expo, that's exactly what the line looked like at the booth for the game. Long lines of zombie gamers pounding on the doors eager to get their hands on the thrilling shooter. When they finally got there? Simply sitting back and watching them play the game it was easy to tell one thing; this shit is fun.