Living up to the multi-faceted meaning of the title, Left 4 Dead features four playable human characters, who have been left behind to survive in a city with a rapidly growing population of people-eating undead. The characters are identical in the way they play, although outwardly they appear largely dissimilar and unlikely to get along well at first. They'll need to trust one another and work together, as it takes teamwork to survive in streets overrun with rampaging zombies. Computer-controlled companions are available for solo players, but online multiplayer co-op games are a main thrust of play. In a standard game, players begin each level in a safe room area, where they can stock up on supplies and agree on a general strategy before moving out into the zombie-flooded city streets.
No place is safe for too long in this game, however, and once the zombies start coming, they keep coming, no matter where the players run or hide -- until the heroes make it to the next safe room, to end the level. The exact progression through each level is not known from the start. A built-in artificial intelligence "Director" analyses the players' positions and creates new challenges on the fly, making each game a little different and adding creepy factor of the unknown. Friendly fire is painfully possible, so players need to be careful where they aim and shoot. Sometimes, in close quarters, a quick melee attack is a safer way to temporarily stave off encroaching undead or knock a hungry zombie off a companion. Each player can carry only one health pack, which can be used for self-repair or to heal a teammate.
Left 4 Dead was developed by Valve Software, built on the studio's Source game engine. In addition to the four-person survival-horror shooter, other available modes of play allow multiplayer competition for up to eight, with one team of four playing as the human survivors and the other four players taking the roles of infected boss zombies. Each boss zombie has a different special power, such as a prehensile tongue or an explosive belly full of corrosive swamp gas, encouraging them to combine their strengths and work as a team, just like the unfortunate human beings they are hunting.
The "Game of the Year Edition" comes bundled with a "Survival Pack" that includes an entirely new "Survival" game mode and two complete campaigns for "Versus" mode.