Left 4 Dead 2
Left 4 Dead 2 is a first-person cooperative video game developed and published by Valve Corporation. A sequel to Left 4 Dead Turtle Rock Studios, the game was released for Microsoft Windows and Xbox 360 in November 2009, for OS X in October 2010, and for Linux in July 2013.
Left 4 Dead 2 is based on cooperatively focused gameplay and Valve's original engine, the same game engine used in the original Left 4 Dead. Set during an apocalyptic pandemic, Left 4 Dead 2 focuses on four new survivors, battling a horde of zombies, known as infected, who develop severe psychosis and act extremely aggressively. Survivors must fight their way through five campaigns, intertwined with safe houses that act as checkpoints, with the aim of escaping at the end of each campaign. The gameplay is gradually changing "AI Director 2.0", which monitors player performance and adjusts the script to provide a dynamic challenge. Other new features include new types of Special Infected and an arsenal of nearby weapons.