Here's the latest video describing the storyline and enemy playablity of the game.
HD - http://www.gametrailers.com/player/24755.html?type=

Street surivival gamepaly HD:
http://www.gametrailers.com/player/24568.html

Valve Software has released its’ world premiere gameplay footage for its coming Half-Life 2 zombie shooter Left 4 Dead. Produced by Turtle Rock Studios.

In this horrifying new horror survival game, a new and highly virulent strain of rabies virus emerges and spreads through the human population with frightening speed. The pandemic’s victims before grotusely disfigured, widely violent psychopaths, attacking the uninfected in sight.

One of the “lucky” few apparently immune to the sickness, you, unfortunately are also trapped in a city crawling with thousands of the bloodthirsty infected. Alone, you’re dead. But together with a few handful of the survivors, you must fight your way to safety.

Using weapons like shotguns, Uzi submachine guns, M16A2 rifles, and other instruments of destruction, you fight hordes of deadly zombies along with three other online players in this multiplayer co-op.

Courtesy of GameTrailers.com (in a World Exclusive), Valve proudly presents the gameplay trailer in high and standard definition formats. Prepare yourself for a scare.

Left 4 Dead will be released into stores and online servers on September 30, 2008.

Gameplay trailer (World Exclusive):

High-defenition – http://www.gametrailers.com/player/31350.html
Standard definition – http://www.gametrailers.com/player/31351.html