From the developer's website: Set in the zombie apocalypse Left 4 Dead 2 is a co-operative, action horror, first person shooter that 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 three horrific and formidable new Special Infected. You’ll also encounter five new "uncommon" common infected including the terrifying Mudmen. The new AI Director 2.0 has the ability to procedurally change the weather and the pathways you’ll take in addition to tailoring the enemy population, effects, and sounds to match your performance.