Edit: Watch your favorite Halforums Heroes play L4D2 on
this playlist!
This one's going out to
@Null who just got L4D2 on the last steam sale, but I figure everyone might get a chuckle out of seeing it.
Left 4 Dead is a cooperative survival horror first person shooter. The game involves four "Survivors" trying to navigate to a goal (usually a safehouse/saferoom) without all getting eaten by zombies.
Left 4 Dead 2 includes all content from Left 4 Dead 1, plus more and enhancements, so it's best to just play the sequel.
Here are the survivors:
Above: Nick, Rochelle, Coach, Ellis
Below: Bill, Louis, Zoey, Francis
The survivors are all 100% identical in performance, and differ only cosmetically (appearance and voice/banter). The survivors on the bottom are from the L4D1 content (starts in Pennsylvania), the above are L4D2 content (starts in Georgia). At one point, the two survivors do cross paths in a certain episode, but we're getting ahead of ourselves. The point is, sometimes you'll be one of the 4 on top, sometimes you'll be one of the 4 on bottom, and it doesn't matter who you pick from a performance standpoint. But I like to be Francis or Coach just because.
Survivors can carry one main weapon, one secondary weapon, one medical kit, one thrown weapon, and one minor item. Left click shoots, right click shoves. More on weapons later.
This game ascribes to the "zombie virus" school of thought... IE, the zombies are not reanimated corpses, they are living humans driven mad and homicidal by a sickness nicknamed the "Green Flu." Thus, it is not necessary to get 100% headshots... you can kill zombies just fine by aiming at center mass.
These are "common" infected.
Common infected typically stand around not doing much, puking on the ground, leaning against walls, or lying in crumpled heaps until they detect a non-infected person. At which point they will run at the person and try to bite and claw and bludgeon them to death.
Don't worry, you're immune to the zombie virus. But you can still be killed by violence.
Anyway, common infected are easily killed. Their strength comes from their numbers, especially when a large group gets into a frenzy.
In addition to common infected, there are 8 kinds of "special infected." They're kinda like miniboss zombies. They are Hunters, Smokers, Boomers, Jockeys, Spitters, Witches, Chargers, and Tanks. They appear randomly and occasionally, and their appearance is usually hinted by a leitmotif - there will be a musical cue that you can hear if you are listening to the soundtrack to tell you what's coming, kind of like how in X-Wing back in the 90s you could tell when more allies/enemies were warping in based on the changes in the soundtrack.
Hunters
Hunters are zombies that crawl around on all fours, and make a distinctive, wet growling sound. They can climb walls and, though they crawl slowly, can suddenly leap quickly over large distances. They will attempt to pounce on a survivor, especially one who has strayed too far from the rest of the group. A survivor who is pounced cannot move or fight back, and the hunter will continue to sit on the pounced survivor, clawing his face off until he dies unless another survivor comes to rescue the pounced. Killing the hunter does the trick, but if you're up close a quick shove (right click) will knock the hunter off his victim immediately and sometimes is a better option to save the survivor faster.
Smokers
Smokers are tall, skinny zombies covered in malignant growths. Weak in melee combat, they can fire their tongue incredible distances. If the tongue hits a survivor, it will then retract the tongue, dragging the survivor to the smoker, where the survivor is then strangled (same rules as pounced by a hunter). When the smoker is killed, he explodes in a cloud of dense, foul smelling smoke that obscures vision and causes survivors to cough uncontrollably (though other than poor vision, it doesn't affect player performance really). Smokers are frequently on top of roofs or in other out-of-the-way areas that they cannot be reached, and their distance makes them hard to kill sometimes. You can immediately free a survivor being dragged by shoving them. In addition to their musical leitmotif, you can tell a smoker is around by their loud, squeaky coughing.
Boomers
Boomers are extremely fat zombies covered in boils. Boomers will attempt to vomit on survivors, which will cover them in Boomer Bile, which will cause a Frenzy of common infected, focused on whoever's covered in puke, and severely impair that player's visibility for 5-10 seconds. When shot, a boomer will explode, covering everyone nearby in boomer bile - so best to shove them away, backpedal to get distance, and then kill them out of explosion range. Boomers are heard to make loud, low groaning noises.
Jockeys
Jockeys are very small zombies that skitter along the ground and hop small distances. They will try to leap onto a survivor, and by yanking their head and hitting them, try to "steer" the survivor into more groups of zombies. They're especially troublesome to kill because it's hard to shoot them without also shooting who they're riding. You can tell one is around by listening for their distinctive hyena-like laugh.
Spitters
Spitters are female zombies who try to keep their distance, and spit giant gobs of acidic goo at survivors. Wherever the spit hits, an area about 10 yards in diameter turns to bubbling, corrosive acid that deals damage quickly and is entirely capable of wiping out groups of unwary survivors who don't get clear fast enough. Killing a spitter also causes a small pool of acid to form where they fall. Spitters hocking/clearing their throat are their auditory cues.
Witches
Probably the second most dangerous single zombie in the game after the Tank, the witch is a female zombie who sits on the ground, loudly crying and sobbing in a plaintive voice. The witch will ignore everything around her, including survivors, so long as she is not disturbed. Things that disturb the witch are: loud noises, bright lights, being damaged, or a survivor being too close for 5 seconds. When you hear a witch crying, turn off your flashlight (F key), as shining a flashlight on a witch will disturb it. When a witch is disturbed, it will scream and launch itself at whoever was responsible for disturbing it, and the witch's attack is a 1-hit kill. Often it's best just to navigate around the witch if you can, but if you have to kill one, make sure you've got big guns and lots of room to backpedal while firing. On lower difficulties, the chainsaw can 1-hit-kill the witch.
Chargers
Chargers will rush a group of survivors, knocking them all flying, and will grab one survivor and repeatedly bash him into the ground until either he or the survivor is dead. Unlike other types of pouncing zombies, the charger is too strong to be shoved off his victim and must be killed to be stopped. A charger bellows like a rhino when he is charging.
Tanks
The tank is the most deadly and destructive zombie. Huge and muscular, he can bash survivors around like rag dolls and throw them incredible distances. He can soak extremely impressive amounts of damage, usually requiring cooperation of the entire team of survivors to take him down. He is fast, he is lethal, and he is usually what causes a group of survivors to get wiped. If he can't reach who he wants to smash quick enough, he can also rip up large chunks of pavement to throw. The Tank's arrival is so important it is the only zombie that causes the soundtrack to immediately change to an entirely different theme, and his hulk-like roars and snarls can't be missed - though usually the music will be your first clue he's coming.
Also, there are various kinds of "uncommon" common infected such as zombie cops wearing body armor (shoot them in the back), zombies in quarantine suits (they are fireproof), zombies wearing clown shoes (their squeaking attracts more zombies), zombie mud men (... you'll just have to see), and fallen survivors (they drop useful items when they die, but they prefer to run rather than fight).
Your goal as a survivor is to make it through this door:
These are saferoom doors, and are the only doors zombies can't open/break. When all living survivors make it into the saferoom and the door is shut, the level is considered beaten.
Weaponry:
Primary weapons:
Primary weapons are your main methods of dealing damage. They consist of shotguns, assault rifles, sniper rifles, machine guns, and grenade launchers. Shotguns aren't good at long ranges, but at short ranges their damage is immense, and at medium range they can take out several common infected at once. Assault rifles do decent damage at all ranges and are good all-round weapons. They don't do as much burst damage as shotguns, but shotguns have to have shells reloaded one by one, so there's balance. Sniper rifles are great at long range, but of marginal utility at close range and not many people choose to use them. Machine guns (M60) and grenade launchers are special weapons that cannot have their ammo replenished, but do massive amounts of damage.
Secondary weapons:
Secondary weapons are what you use when you run out of ammo for your primary. They come in two flavors - pistols and melee weapons. There are two kinds of pistols - regular automatic pistols that you can dual wield if you find an extra one but don't do much damage per shot (but are better than nothing), and the big pistol (D. Eagle 50 cal) which does more damage but is unwieldy and only holds 7 shots and can't be dual wielded. There's a huge variety of melee weapons ranging from bats and machetes and fire axes to katanas and guitars and everything inbetween. Some are more effective than others (most people like the katana best). There is also a chainsaw which is insanely effective at killing anything near it, but it has limited, unrefillable fuel. You can still right click to shove while using a melee weapon.
Medical kits:
You can carry one of the following: a first aid kit, or a defribulator. A first aid kit will let you heal yourself or another survivor by bandaging them, restoring them to (mostly) full health. Bandaging takes 5-10 seconds to do, so don't do it in the middle of a fight. If a survivor is "downed" 3 times without receiving first aid, he or she will die. Defribulators will revive a dead player by shocking their corpse. Most people go with the first aid kit, only carrying defribulators when no FAKs are available.
Thrown weapons:
Two kinds: Pipe bombs and molotov cocktails. Pipe bombs have a smoke detector alarm attached, which is activated when thrown. Common infected will chase the beeping bomb, gathering around it to be blown up after a short delay. Molotov cocktails will engulf a 10 yard diameter circular area in flames for approximately 30 seconds, dealing massive damage to anything in that area, and survivors and zombies who are set on fire will continue to burn for a little while even once clear of the fire. These weapons are usually held in reserve as your "get out of jail free" cards when facing a huge frenzy of common infected.
Minor items:
Again, two kinds: pain pills or adrenaline shot. Pills will give you a large amount of "fake" healing, a dotted line on your health bar that will slowly drain away over 10 minutes or so. If you're low on health and don't have a first aid kit (or just want to save it for later), pills will usually do the job to keep you from being downed. Adrenaline shots will "fake heal" a small amount of your bar, but will also increase your speed and melee damage. If you intend to whip out a sword and wade through an oncoming rush of common infected, Adrenaline will really help you get through it.
Overview -
So, basically, your survivors are trying to reach safety. Generally this will involve 3 or 4 levels of moving from saferoom to saferoom, usually with some difficult halfway points that involve doing something noisy that provokes a frenzy in order to move forward (for example, opening an emergency door that sets off a fire alarm). The final culmination of a game comes to a Last Stand - where the survivors must hold out against non-stop waves of oncoming common and special infected while waiting for rescue or while trying to accomplish their own rescue. When a survivor's health reaches zero, he is "downed," and cannot move but can try to shoot with pistols. Another survivor can get a downed survivor back on his feet in about 5 seconds by holding the E key while targeting him. The downed survivor will be picked back up with 1 health. If a survivor is downed 3 times without receiving first aid, they die, so it's usually best to immediately bandage someone after they've been picked back up. If all four survivors are killed, they have to start that level over again.
That's basically the deal.