Left 4 Dead 2

[i]From the developer's website:[/i]

Set in the zombie apocalypse, Left 4 Dead 2 (L4D2) is the highly anticipated sequel to the award-winning Left 4 Dead, the #1 co-op game of 2008.

This co-operative action horror FPS takes you and your friends through the cities, swamps and cemeteries of the Deep South, from Savannah to New Orleans across five expansive campaigns.

You’ll play as one of four new survivors armed with a wide and devastating array of classic and upgraded weapons. In addition to firearms, you’ll also get a chance to take out some aggression on infected with a variety of carnage-creating melee weapons, from chainsaws to axes and even the deadly frying pan.

You’ll be putting these weapons to the test against (or playing as in Versus) three horrific and formidable new Special Infected. You’ll also encounter five new "uncommon" common infected, including the terrifying Mudmen.

Helping to take L4D’s frantic, action-packed gameplay to the next level is AI Director 2.0. This improved Director has the ability to procedurally change the weather you’ll fight through and the pathways you’ll take, in addition to tailoring the enemy population, effects, and sounds to match your performance. L4D2 promises a satisfying and uniquely challenging experience every time the game is played, custom-fitted to your style of play.