Left 4 dead is a zombie survival game series pitting you and up to 3 other allies against the horde in several modes of play. The modes of play include campaign, survival, versus and single player.

Single player and Campaign have you primarily combating the AI while traveling through a variety of terrain, Campaign being the multi-player coop component. Survival takes you and your allies against a forever growing and overwhelming horde, timing how long you really can survive against insurmountable odds. Versus mode places you and another team in each level of a campaign, taking turns being the survivors and the infected horde. Which team can do the best as survivors when facing human players of the horde is up to you.

When playing the survivors, you pick from a list of 4 survival heroes, Each one with their own catch phrases and attitudes. As you progress through the campaign levels you find various weaponry and supplies randomly strewn across the map. Your team must balance supplies, making sure that survival is a team effort and not a solitary effort. You really can't survive against what awaits you by yourself, so choose wisely who consumes what.

When playing the infected horde, you randomly are assigned one of several types of special zombies with their own special characteristics. The key to your success as the infected is to coordinate your attacks with your allies. Your efforts are best spent trying to do as much damage as possible in the slim life period you get. The infected are not particularly strong individually, your strength comes from combined efforts, which if properly performed pay off in the end.

Left 4 Dead's strengths lie in the variety in how the game plays out. The AI "director" reacts appropriately to how the survivors are progressing through each stage of the campaign. Making it harder in areas they are having difficulties in, and placing helpful items in random locations, so you never quite have the same experience as before.