Coming exclusively to Xbox 360 and PC, L4D2 promises to set a new benchmark for co-operative action games and become one of 2009's marquee titles.

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.

In addition to the new campaign, Valve is also planning to unveil a few more of the 20-plus new items coming this November when the title launches worldwide on the Xbox 360 and PC.

The Spitter is the second new Boss infected from L4D2 revealed thus far (the Charger was revealed at E3). The female Spitter has an area attack that can split up Survivors or flush them out of their hiding spots. At least one more new Boss infected is expected to be revealed before launch.

In addition to the new campaign and boss monster L4D2 also includes "Mudmen," the "uncommon common" exclusive to the Swamp Fever campaign, and a few more of the 20-plus new items coming in the full product (cricket bat, AK47, and grenade launcher).

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.