its for ARMA 2 + Operation Arrowhead, and as such is graphics heavy. what makes this mod so entertaining is your only goal is to survive. There is no L4D style over it where you go in guns blazing while cracking oneliners, you try and sneak past the zombies, conserve ammo and if you do have to shoot one you better be sure to do it quietly, as the zombies respond to sound and light.
While Im praising it, it is only in alpha/beta state and as such its still very rough around the edges, but even in its current state its still one of the best zombie games ever made. think Resident evil 1 combined with stalker and you have the gist of it ^^