Left 4 Dead use to be a highly competitive Esport. The game puts four humans against a horde of zombies. Zombies are AI, while human players can control four Special Infected with special abilities in PvP (Hunter, Smoker, Boomer, and Tank. The goal of Left 4 Dead for the Survivors is to help each other make it through a level to safety. Infected players must cooperate to stop them.
There are some crazy strategies to prevent your opponent from getting to the end. The co-op mode versus AI though is super easy, but still really fun!
Left 4 Dead 2 came around and really watered down the game where at one point the special infected were so crazy under powered it destroyed the pvp scene.