Gameplay Modes

There are 5 Gameplay Modes in Left 4 Dead, and 7 Gameplay Modes in Left 4 Dead 2.

Campaign
During Campaign, also known as Co-op, up to four players work together to try to reach the end of the campaign by fighting their way past large numbers of AI-controlled Infected. There are four difficulty levels: easy, normal, advanced and expert. Each chapter ends in a Safe Room, a checkpoint triggered when all living Survivors, once inside, close the door behind them.

In Campaign mode, one or more players play as the Survivors, with the rest of the four filled in with AI-controlled "bots". The Survivors play through each chapter, making their way from safe room to safe room. The last stage in each campaign has an expanded ending called the Finale, which usually ends with players escaping with vehicles, like cars, helicopters, etc.

Single-player
Single-player is a gameplay mode with only one player controlled character. The player assumes control of one of the Survivors, and all the other characters are AI controlled. No other player can join a Single-player game. Other than that, the same rules as campaign apply here.

Split Screen
In Split Screen, two players on the same console take control over two Survivors, and the screen is split vertically, although it can be changed to horizontal in the options menu. The two players can also play online while using split screen.

This game mode is exclusive to the Xbox 360 version of Left 4 Dead, but may be accessed in the PC version if you have a controller for the second player and modify some files. Here is a guide to how to play splitscreen on the PC. Note that the original poster forgot to mention something in his post. Plugging the Xbox controller in and out during the loading screen is NOT the only way to set the Xbox controller to player 2. During gameplay, you can also unplug and plug the Xbox controller back in within one second to set the controller to player 2. In fact, the second method proves to be more effective with several people.

Versus


Versus is the basic competitive mode for the Left 4 Dead series. 2 separate teams of 4 players take turns playing as the Survivors and the Infected competing for the most points. In Left 4 Dead, points are only awarded to teams playing as the survivors, however, in Left 4 Dead 2 teams playing as the infected get points for incapacitating survivors. Before a game starts the lobby leader chooses a specific campaign to play and the players can choose which team to play on by choosing whether to start as infected or survivors. For help as Infected or Survivors, review some tactics.

Survival Mode


Survival Mode was released in the "Survival Pack," which came out on April 21st, 2009. The point of Survival Mode is to hold out for the longest time, with times being saved and virtual medals being awarded for surviving for certain amounts of time. It features sixteen maps, fifteen of which are taken from existing campaign levels, and one new map which has been called The Last Stand. The campaign levels have been edited to remove things such as closets and other small choke points often exploited by the Survivors in crescendo events and finales.

In Left 4 Dead 2, Survival Mode is back, this time included with the release of the game. The point is still the same, and the maps are still converted crescendo events.

Scavenge Mode


Scavenge Mode is a competitive gameplay mode in Left 4 Dead 2. It is a round based game in which Survivors have a limited amount of time to find up to 16 gas cans to fuel up a generator (or car), while fighting against player-controlled Special Infected much like in a Versus game. After all the survivors are incapacitated or the time runs out, the teams switch sides. Which ever team collects most gas cans wins a round and which ever team wins the most rounds wins the game.

Realism Mode
Realism mode can be played on any difficulty setting. This mode removes the auras usually shown around players through walls. Also, the auras around items are only visible within a few feet, making the game require more communication and teamwork. Realism mode also makes bodyshots less effective as common infected can take more damage. Rescue closets are removed, making the defibrillator the only way to revive dead Survivors. Witches kill instantly and are notably harder to cr0wn. Overall, this gameplay mode was created to take the teamwork factor that made the Left 4 Dead series famous to the next level.

Unreleased Game Mode
A new mode of gameplay was announced to go along with the upcoming campaign, The Passing. The game mode is currently unknown, though it's likely an 8-player co-op as Valve has hinted.