The article below has been taken from the official Left 4 Dead 2 Blog.
The first game add-on for Left 4 Dead 2 brings the original Left 4 Dead (L4D1) Survivors down south for a meeting with the L4D2 cast, while delivering new single-player, multiplayer and co-operative gameplay for the PC and Xbox 360.
The Passing also introduces a series of weekly game mode events dubbed “Mutations.” These week-long runs of new gameplay modes range from “Realism Versus” mode to “Chainsaw Massacre,” which gives all players chainsaws with an unlimited supply of gasoline. There are over 20 Mutations planned, each playable on all L4D2 Campaigns. Mutations are exclusively available to owners of “The Passing” DLC.
In addition, “The Passing” offers a new co-operative challenge mode of play, support for infected bot play in Versus, a new “uncommon common” zombie class (the fallen survivor), melee weapon (golf club), and firearm (M-60).
Available for 560 Microsoft Points on Xbox 360 and free on the PC, “The Passing” takes place just after the Dead Center campaign of L4D2. Set in a small town in rural Georgia, players assume the role of the L4D2 Survivors as they meet with the L4D1 characters.
Exclusively available for Xbox 360 and the PC, L4D2 sets a new benchmark for co-operative action games. The title adds melee combat to enable deeper co-operative gameplay, with items such as a chainsaws, frying pans, axes, baseball bats, and more.
With 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.
Finally, with new Survivors, boss zombies, weapons, and items, Left 4 Dead 2 offers a much larger game than the original, featuring more co-operative campaigns, more Versus campaigns, new Survival maps, and the new competitive game mode, Scavenge.
To celebrate the launch of “The Passing” DLC this Thursday Valve employees will be playing on the PC between 11am-5pm PDT and then on the 360 from 7pm-11pm PDT using special accounts. To play with someone from Valve just friend one of the following:
L4D2_DEV_1, L4D2_DEV_2, L4D2_DEV_3, L4D2_DEV_4, L4D2_DEV_5, L4D2_DEV_6, L4D2_DEV_7, L4D2_DEV8, L4D2_DEV_9, L4D2_DEV_10
On the Xbox 360:
L4D2 DEV 1, L4D2 DEV 2, L4D2 DEV 3, L4D2 DEV 4, L4D2 DEV 5, L4D2 DEV 6, L4D2 DEV 7, L4D2 DEV 8, L4D2 DEV 9, L4D2 DEV 10