The premise of Left 4 Dead is quite simple and shares the same basic concepts across all four game modes. As a character in a B-grade horror movie, you are part of a group of four survivors who must travel through zombie-infested environments in search of rescue.
Each of the four stand-alone movies consists of five maps that your group of survivors must advance through, stopping at safe houses at the end of each map, where they can find supplies and weapons.
In the final map of each movie, your group of survivors must withstand a massive attack by the infected called a finale. If they survive the finale, they can board a rescue vehicle and escape, bringing the movie to an end.
The basic premise of survivors traveling from point A to point B is carried over through the following game modes.
Co-op Campaign
During co-op play your teammate's names appear above their character, making it easy to identify and address the proper player.
In the campaign mode, you and up to three other players can choose one of the four movies and play through it cooperatively. There are always four survivors while playing in this mode, even if only two of them are controlled by actual players.
Any unassigned player slots are taken over by AI-controlled survivors. But new players can join at any time, taking the place of one of the AI-controlled survivors. Such co-op sessions can be played online or over system-link on a LAN.
If you want to join a match already in progress use the Quick Match option. This automatically connects you to a game, allowing you to jump in and join the action within a few seconds. If you want more control, choose the Custom Match or Play with Friends option.
Choosing the Custom Match option allows you to specify what movie and maps you want to play on. The Play with Friends option takes you to a lobby screen showing all matches your friends are currently playing—select one and join in.
Offline Co-op (Splitscreen)
Two players can play in splitscreen-the other two survivors are controlled by A.I.
If you connect two controllers to your Xbox 360 you can play through the campaign in splitscreen mode. This mode supports two players and splits the screen in half, with each player controlling a survivor in a separate partition.
In the options menu you can select whether you want the screen divided horizontally or vertically. If playing on a widescreen television or monitor it’s best to split the screen horizontally. This helps preserve your peripheral vision while playing.
Single-Player
You must lead your A.I. controlled teammates when playing single-player, which often makes you an easy target for the infected
In the single-player mode you play the role of one of the survivors—the rest of the survivors are controlled by the AI. When starting a single-player game you must first choose from the movies and their individual maps.
Once one is selected, the game begins and continues until you reach the finale at the end of the movie.
During the single-player mode the AI bots always follow your lead, so it’s up to you to set the tempo for the advance. This often means you take the brunt of the attacks, so keep a close eye on your health.
If you die, you must start the map over from the beginning. If your AI teammates die, they respawn in closets and are released when you open the door.
Versus
In versus mode, the survivors should strive to reach the safe house at the end of each map as quickly as possible.
Versus is an adversarial game mode pitting the survivors against the infected. Only No Mercy and Blood Harvest can be played in this four-on-four mode, offering 10 maps total.
The gameplay is nearly identical to that of the other modes, with the survivors tasked with making it from safe house to safe house and ultimately escaping after surviving the movie’s finale.
It’s the job of the infected team to stop the survivors. Unlike in the other game modes, in versus the survivors cannot respawn, but the infected team can. This provides a unique twist to the game mode, forcing the survivors to work together and watch each other’s backs.
While the survivors spawn as the main protagonists, the infected team members take on the roles of the special infected. At any given time the infected team always has one Boomer, two Hunters, and one Smoker on the map.
Who spawns as what is random, determined by the director.
At some points in the map, one player on the infected team is given the chance to spawn as a Tank, providing the team with an extra boost in offense. The Witch is not playable by the infected team, but Witches do make appearances on occasion.
Witch spawns are determined by the director and are never in fixed locations. Still, the infected team should use appearances by the Witch to bolster their numbers during coordinated ambushes.
During these matches, each team gets the chance to play as both the survivors and the infected on each map. So after the survivors have escaped or died in the first round, the same map is replayed and the two teams switch sides, with the former infected taking on the roles of survivors and vice versa.
Playing as the survivors is completely different from playing as the infected, and winning requires different skills and tactics. Regardless of which side you’re playing, communication and teamwork are always essential.
Ghost Mode
While you're in ghost mode the survivors can't see you. But you must move to a spot outside their line of sight before you can spawn and attack.
While playing as the infected, players begin in ghost mode, which allows them to pick their own spawn points. During this phase, the infected can wander around a map, completely invisible to the survivors.
While in ghost mode players can use infected-only climb points (look for a series of claw icons) and pass through closed doors.
The infected team can spawn anywhere they want as long as they’re a few meters away from the survivors and outside their line of sight. Once these requirements are met, the infected can spawn by pressing the fire button or key. But once they spawn, all normal rules apply.
They can be spotted and killed by the survivors, and they can’t pass through doors—or open them. Closed doors must be broken down with melee attacks, so be careful where you spawn. Breaking down a door may give away your position and lead to a quick death.
Spawning also causes the infected to make the telltale growls, grunts, and hisses associated with each variant. These involuntary vocalizations not only give away an infected’s position but also warn the survivors as to what type of infected is nearby.
So to avoid giving the survivors time to react, try to spawn just before attacking. Coordinating spawns and attacks with teammates is the best way to take down the survivors.
During finales, ghost mode is disabled, and you randomly spawn somewhere around the finale site.
Versus Scoring System
At the end of each round, the survivors' score is calculated. Scores are carried over from maps to map until the finale at the end of each movie is complete.
So how do you determine who wins a match in versus mode? After playing a round as the survivors a score is calculated based on four criteria:
Average Distance Traveled
The points awarded in this category are based on how far your team traveled during the round. If your team made it all the way to the end of the map and reached the safe house, you’re awarded the maximum 100 points.
But if your team made it through only 37 percent of the map before being stopped by the opposing team’s infected, you get only 37 points. The percentage of the map your team completes determines this score.
Health Bonus
This bonus is determined by averaging the hit points of the survivors who made it to the safe house—survivors who were killed en route are not part of this average.
So if everyone makes it into the safe house with full health, 100 points are awarded. Sometimes teams heal up before closing the safe house door to try to boost this bonus.
Survival Multiplier
Once the average distance traveled and health bonus have been added, the score is multiplied by the number of survivors who made it into the safe house at the end. If all four survivors made it in, the score is multiplied by four.
If only one survivor made it, the score is multiplied by one and thus has no impact. If nobody survived, the score is not multiplied by zero. Rather, the score remains untouched, with no multiplier applied.
Map Difficulty Modifier
Each map is assigned a predetermined difficulty modifier. The easiest (or shortest) maps have a modifier of 1, and the hardest (or longest) maps are given a modifier of 2.
The rest of the maps fall somewhere in between, sometimes rated as a 1.5 or 1.6. Whatever the modifier is, it is then multiplied by the score, giving you your team’s final score for the round.
So what’s a good score? Usually posting a score close to 1,000 points per map is considered a praiseworthy achievement. But ultimately it all depends on how well the opposing team performed in their turn as the survivors.
While no points are awarded when playing as the infected, stopping the opposing team’s survivors is critical, preventing them from posting a high score.
Killing even one survivor can have a dramatic impact on the final score, especially in close matches, as it robs the opposing team of that vital survival multiplier.
So don’t fool around while playing as the infected. Stopping the opposing team is just as important as reaching the safe house when you’re playing as the survivors.