A great multiplayer experience that requires teamwork to survive a zombie apocalypse.
Each level is setup the same way, you begin in what's called a safe house and within each one is four health packs (used to heal yourself OR a teammate at any given time), ammo (placed for when you need to restock), and lastly the choice between a submachine gun and a shotgun. As you progress through the level you'll encounter different types of zombies that are unique in the way they attack you. For example the zombie with the title of the "Smoker" who throws his tongue at you and drags across the floor only attempting to strangle you, which can easily be broken out of with the help of an A.I. bot (if you're playing cooperatively with a friend's) simple jab at your body. Each infected type is unique and they each have abilities that others don't. Though there is only ,about, four special infected (including the infamous Tank), they still stir their own trouble in each level. Each time you play survival or campaign zombies are setup in different places making it impossible to guess where they will come from next, Left 4 Dead is focused mainly on the teamwork. If you are playing through the game alone you may be disappointed by the A.I.'s stupidity sometimes, but there's a points where they do shine and save the day.
Multiplayer is a very fun experience that pits the survivors , who must play through a normal campaign, against the infected in a 4 vs. 4 battle. After one chapter of the campaign the two teams filp-flop and the humans who just got to be survivors now get to be zombies and so forth, which continues so forth. The four human players on the infected team get to play as one of the three special infected (not including the Tank because it only comes at certain parts in a level). The survivors are basically playing a campaign level, trying to get from safe room to safe room until the end of the campaign. Zombies must do whatever they can to prevent the survivors from making it anywhere. Survivors rack up points based on their health, kills, etc. at the end of each level, while zombies get points for just attacking the humans. At certain points within each level a "tank" while appear which is a HUGE zombie that runs wildly at the survivors with its massive strength. A majority of reasons survivors lose is due to the condition the tank leaves them in, if it even spares their lives.
In the end, this game isn't something you can rent because you will keep coming back for me. Hopefully the next installment in the series lives up to this ones standards.