Gabe Newell: Left 4 Dead is All About Directing Action

Left 4 Dead will live or die by its artificial intelligence. But it won't be the AI driving the undead that make or break the game, it will be the computer intelligence driving the game's direction.

Talking to a gathering of journalists last week, Valve's Gabe Newell talked up the company's upcoming co-op survival horror shooter.

The game is based on four movies each of which gamers play through as survivors trying to escape an army of the undead. The game will also support an infected versus survivor mode and a split-screen cooperative mode.

In Left 4 Dead gamers live out a horror movie, but to do that the game has to be able to react to the situation, Newell said. The developers managed to do that by having the game procedurally generate character performance, pacing, lighting and music.

This means that depending on how you play and how those with you play the game plays out differently every time/

For instance, Newell showed us a situation where the four survivors of the game barely make it to a gas station near a safe room. The characters, all near death, are confronted by a small number of zombies which slowly appear out of pockets of shadow.

When shown a second time, with the players in much better shape, with more ammo, the zombies stream out of the four corners of the screen coming at the players from all sides until one of the group blows up the nearby gas station, sending it's roof first floating up on a ball of flame and then crashing down among the walking dead.

"The director is a bunch of AI," Newell said. "It sets the stage for climaxes, the pacing. It writes script for your character, creates the drama around you."

I experienced this first hand when playing through a level of the game first hand. Lured away from my group by a zombie, when I ran to find them again I found myself facing the city of zombies by myself and quickly killed. It was a classic "Don't go in there" moment for me.

Newell says that's the brilliance of the game .

"The game is going to play different every time," he said.