Left 4 Dead Design Theory

Left 4 Dead is a Co-op single, and Multiplayer game. In order to better understand the design behind L4D, you'll need to think diversely in both fields of Level Design.

• A good map is Fun to play on, and Fresh. The best maps can run on a 24/7 server without getting boring even after the second or third reload.
• A good map accommodates all player ranges of skill, and ability. If the player is failing or having a hard time progressing, neither should the map. Always make the map universal to all kinds of Players.
• A good map is designed, not simply constructed. If all you are doing is re-creating the surface appearance of another map, you're highly unlikely to create something worth playing in its own right.

Starting Off

Left 4 Dead takes place in a zombie apocalyptic Setting. While the rest sprawls through various other scenery. That being said, L4D follows a pseudo Counter-Strike: Source type system. The main flow of the game is directed by an overruling AI, called the info_director. This Director controls waves of enemies, and Dynamic Difficulty.

Environment

Your first goal before starting should be to think like a zombie. However without the the idea that your goal is to kill the survivors. The game heavily relies more on the actual waves of zombies influence rather then the players. Because of this zombies can reach just about any height, if of course there is a way to climb up to it.

When thinking about the kind of environment you would like to design, consider the kind of situations the player might find themselves in. Because no one has really lived an actual zombie apocalypse, it's up to you to continually playtest through each of your areas to understand natural decisions any survivor may make. The waves of zombies are dynamically controlled in each section of your map, meaning any real area can be dangerous because of this.

Left 4 Dead excepts non linearity because initially your designing your map for two parties: The survivors and the Infected.