The definitive co-op experience.
Left 4 Dead 2 is a co-op survival game. You must endure one of the many campaigns with the help of your friends through the internet -- these friends can also be CPU-controlled bots. The campaigns are divided in three, four or up to five acts. In between these acts there's a safe-house where health kits and ammo is found; a quick rest and back to action. This is the primary formula of the main game. In the campaigns you're sure to find many zombies to kill, but going Rambo on them is not an option, a single person is easily overwhelmed. Teamwork is essential to succeed, especially at higher difficulty level where things get ugly pretty fast.
What makes Left 4 Dead 2 a blast to play is certainly the co-op, you need your fellow players and they certainly need you as well. If you and your friends are up for a game just create a lobby and call them up, decide game settings and game on. If you don't know anyone who plays it but still doesn't want to surrender to bots you can easily find a match online with strangers. Be it a quick match in whatever map and difficulty or getting specific; it's up to you. You can connect to an official server, a dedicated or hold a local server.
Up to 4 players are allowed to participate and if someone bails out for some reason a bot takes place until someone else decides to join in. The bots are actually quite helpful, they won't get on your way but won't perform key campaign actions like filling up a car's tank with gas or grabbing mandatory quest items, it's up to you to do that, and in a co-op game it can get tricky doing all alone taking an excessively long time, which can mean death in the end. At least the bots are good enough so they won't hit you accidentally, something common playing with humans. The AI is very well calibrated and most of the time they have the right set of priorities, always steadfast to help you out when in need.
To fight the infected (arguing whether or not they're zombies is irrelevant) guns are used, anyone familiar with video-game knows them by now. Pistols, rifles, shotguns, precision rifles and all the expected arsenal. Melee weapons are included in case you need to get physical, and they're useful since most times they'll one-hit kill any common infected. In addition to the common infected which are found in hundreds, there's the special infected, enemies with several unique features that make them much more deadly foes. Fat guys who vomit zombie-attracting liquid, monsters who rush onto you and pound you repeatedly to the ground, crawling infected that sneak up and mount on you scratching your face to bits. Chances are that if you're caught by one of these special infected, one of your team mates will have to come up and save you, otherwise it's sure death.
When you die you die, your fellow survivors will have to cope with one less player around. Though death is not irreversible, if you die after a while you appear locked in some random room along the way and if someone releases you then you're free to go. It only happens after a while and one less integrant on a team could make a difference. Health kits are also not unlimited and making good use of them is essential. When you're low on health you start walking slower and gets more susceptible to go down, to aid when under these effects pain pills can be ingested, they won't recover health but will revert the symptoms for a limited period of time. Adrenaline Shots also works on your health and give you a boost in adrenaline helping you by being able to run faster, use items quicker and not lose speed by being attacked by infected.
When your health reaches zero you fall on the ground unable to move until someone comes and pulls you back on your feet. A secondary health gauge exists only for this moment and the longer you stay down the more you lose health in this state of incapacitation. If this secondary gauge reaches zero then you're dead for good, only later on someone might get you back to the game. When you're down you hopelessly open to attack but you do have the option to use your pistol to keep infected away and extend your life until someone comes. The pistol is available at that point even if you exchanged your pistol for a melee weapon, which can't be used. Heavier weapons like shotguns and rifles can't be used while incapacitated.
In Steam's PC version you get to play on 6 different official maps, a beta map (not sure when it's going to get its final version), and two recurring maps from the first game. The downloadable content is unlocked. They're all pretty good maps but after a while replaying them might get tedious. If that ever happens there's websites entirely focused on hosting user-made maps that adds practically limitless replay value to it. Many have professional feel to them and with the exception of some uneven optimization and some bugs many feel like they could have been made by Valve themselves. If you don't get enough of the formula, there's surely enough maps available to keep you playing Left 4 Dead 2 for a very long time.
But the main game is not everything Left 4 Dead has to offer, several different game modes are available as well. In Versus mode eight players alternate between playing as the survivors and the special infected in each act of a campaign. A scoring system tells which team is the winner at the end. Playing as the special infected adds completely new gameplay mechanics, they're all thoroughly explained as you start. Your mission as the survivors is the same as always, reach the safe house. Your mission as the infected is to prevent that from happening and kill the survivors. Special Infected respawn after a brief period after death; the same can't be said about the survivors.
In survival mode a team of 4 players selects a location and strives to survive the most they can. Swarms of infected will relentlessly assault the players, including many Tanks, gigantic monsters that are hard to kill but easy to get killed by. Depending on how well the team goes a medal is awarded. Gold, silver, bronze, or no medal at all. The Scavenge mode is similar to Versus, though the survivor team must find gas cans to fill a generator or a car. The winner depends on how many cans are recovered and how long it took. The team playing as the infected must thwart the survivors' plan at all cost.
The Mutation game mode is pretty peculiar, it actually depends on the week you're playing, every week it changes and generally revolves around modifications on the main game like playing only with special infected as enemies or having to carry a gnome through the whole campaign. There's also the Realism mode, it actually enhances both the main game and the versus mode, it adds handicaps like disabling the glow effect of your allies and usable items, zombies taking less damage on the neck down, and no later on come back after you die, when you die you're out until the end.
Left 4 Dead 2 is presented like a movie, each campaign flows into the other. Each frustrated attempt of escaping culminates into another struggle for survival. The survivors of this game co-exist with the survivors of the first game, even some interactions happen along the way. The conversations between the characters during the campaigns change depending on who the player controls and what actions are taken. They do add depth to the characters. Though the story is extremely secondary and what shines is really the co-op. If co-op is your thing know that this is one of the best examples found in a game. It's a game where you actually need your allies, and communication can save you from a lot of trouble.
Left 4 Dead 2 adds enough new stuff, it adds new campaigns, new characters, new weapons and game modes; though some might say it's not worth the purchase if you have the first one since the gameplay is indeed the same. This became the definitive survival game out there. As a co-op game no other comes close. The campaigns are addictive enough to keep you playing for a long time. The gameplay is well constructed and will satisfy mostly anyone fond of first-person shooters. The fact this is not an average FPS actually opens space for people who dislike the genre, but enjoys survival, zombies or co-op games. Playing with friends is especially fun, but playing with strangers and bots can be awesome too. The fact that there's websites dedicated to user-made campaigns raises the replay value immensely. Valve once again delivers a good experience and a constant updated game that deserves a play.