Left 4 Death -

The franchise is defined by its emphasis on teamwork and cooperative play. The AI Systems of Left 4 Dead - Akamaihd.net

is a renowned cooperative first-person shooter (FPS) survival horror video game franchise developed by Turtle Rock Studios and published by Valve Corporation . Set in a post-apocalyptic environment, the series follows four "immune" survivors who must navigate through hordes of "Infected"—humans transformed into aggressive, feral creatures by a highly contagious viral strain known as the "Green Flu". Core Gameplay and Mechanics Left 4 Death