Left 4 Dead
In Left 4 Dead, four humans, Francis, Zoey, Bill, and Louis, had the bad luck to land in the middle of a zombie-infested zone, and are now trying to survive the apocalyptic pandemic by getting to the evacuation point. The game contains several scenarios which are all divided into several chapters with the goal to reach the safe room, and hundreds of zombies in-between.
The doors to the safe rooms can't be opened by the infected once closed and they contain weapons (shotguns, sub-machine guns, etc.), medipacks, and ammo for the survivors to restock before the next part of the journey. Closing the door to a safe room won't complete the chapter and load the next one until all the survivors still alive are inside, so the team needs to stay together, otherwise they will have to decide whether they leave a friend behind or fight a hopeless battle at the safe room door.
If a survivor is too badly damaged, the character goes down but is neither immediately dead nor defenseless. The character still can shoot with a pistol at incoming zombies to make it easier for teammates to help them up. This is especially important when one of the special zombies such as the Hunter, who can jump great distances and immediately down his target, has a survivor in his grasp. If the zombie isn't killed in time, the teammate will be dead.
Other special zombies include the Tank, which is a huge mutated zombie that packs a serious punch and can take a few hundred bullets before it goes down, as well as the Boomer, which vomits on a survivor to attract a horde of zombies to them. Such things as car burglar alarms going off or other noisy scripted events during the course of the campaigns can also attract massive zombie hordes.
While the campaigns can be played either with AI-controlled teammates or with other human players in co-op, the multiplayer also features an additional game mode called "Versus". The basic premise remains the same with four players needing to get safely to the safe room, but at the same time four other players are randomly assigned the roles of one of the special zombies with the obvious goal of helping the normal, AI-controlled infected getting rid of the survivors. The zombie players have the advantage of being able to spawn almost anywhere on the map as long as it's out of the sight of survivors, and they can see them through walls when they make noises, but they are otherwise easy to take down if noticed early (except for the Tank).
