L4D2 promises to set a new benchmark for co-operative action games and become one of 2009's marquee titles, adding melee combat to enable deeper co-operative gameplay, with items such as a chainsaw, frying pan, axe, baseball bat, and more.

Nearly a half million members of the Left 4 Dead 2 (L4D2) community have voted to add a permanent new Mutation (aka game mode) to L4D2; Realism Versus. Realism Versus combines the rules of Versus and Realism Modes to create a Versus game that requires the best in Survivor teamwork.

With the release of the DLC "The Passing" last month, L4D2 has seen weekly new Mutations released every Friday.  The excitement and response to Realism Versus was so overwhelming a Poll was added for the in-game blog which simply asked: "Should the Mutation be permanent?"

This week's Mutation is "Follow the Liter." The rules of Scavenge have changed. Only one group of cans spawn at a time, so survivors know exactly where to go. There is only one problem; the Infected know exactly where they are going.

The weekly Mutations are available to all owners of Left 4 Dead 2's "The Passing" DLC, available on PC and Xbox 360.

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 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.