Left 4 Dead (hereafter L4D) is a multiplayer first person shooter that places the human survivors against the infected (zombies). Players team up either against the AI controlled opponents, or in a VS campaign with opposing players controlling the special infected. In either case, usually a thousand or so common infected will be killed during a campaign.
The game seeks to give a cinematic experience. It uses techniques from film (such as vignetting and film grain) to give the look of a movie, it opens the levels with preview posters as loading screens and scrolls ending credits on the completion of a level.
Use of Procedural Content Generation Methods
L4D does not have scripted spawn locations. Instead, the "AI Director" chooses points outside of the survivor's line of sight to spawn the zombies. This increases replayability since survivors cannot anticipate their position. By controlling the rate of zombie spawning, and looking at what the players are experiencing, the AI Director seeks to give a consistently exciting experience without overwhelming the players. Powerups such as extra pistols etc. are also placed by the AI Director, though it seems that there is less variation on their position.
Fragments of the music in L4D are performed conventionaly, then mixed and arranged dynamically based on the state of the player.
In game objects such as cars or zombies are formed by instancing of in-game entities, allowing thousands of possible results without storing thousands of models and textures. This system gives enough control that the number of hospital patient zombies is higher in a hospital area, but the patients will have different faces.