Set for release on November 17, the title adds melee combat to enable deeper co-operative gameplay, with items such as a chainsaw, frying pan, axe, baseball bat, and more.
Introducing the AI Director 2.0, L4D's dynamic gameplay is taken to the next level by giving the Director the ability to procedurally change weather effects, world objects, and pathways in addition to tailoring the enemy population, effects, and sounds to match the players' performance. The result is a unique game session custom fitted to provide a satisfying and uniquely challenging experience each time the game is played.
Featuring new Survivors, boss zombies, weapons, and items, Left 4 Dead 2 offers a much larger game than the original with more co-operative campaigns, more Versus campaigns, and maps for Survival mode available at launch.
Apparently Valve is tweaking the mechanics for the sequel. The original A.I. Director gave Left 4 Dead refreshingly unpredictable enemy placement, and it's promising to see this expanded into other areas of the game -- though I am skeptical as to whether the new weather effects will affect the mechanics in a terribly meaningful way.
Currently there's a trailer on Left 4 Dead's home page: http://www.l4d.com/
