4. Left 4 Dead
Left 4 Dead was developed by Valve so you know straight off the bat that you are going to get one hell of an awesome game. You got put in the shoes of one of four survivors from a zombie outbreak who had to battle through various missions and scenarios to escape the city in one piece. The emphasis on teamwork was the main aspect of the game, making it a really enjoyable online experience when you had the right people- the right people being those who actually cooperated and listened instead of going all Rambo on a level. The zombies in Left 4 Dead also packed a punch, they weren't your slow, Resident Evil types, they could come running at you and beat you into submission in a matter of seconds on the higher difficulties. The game also had Special Infected too which would try and hinder your progress at every opportunity. You had the Smoker who could use his long tounge to incapacitate you, the Hunter who leaps onto you and clawed you to death, the Boomer who when killed, released goo that attracted the normal zombies and finally- the Tank, a massive brute who took some serious punishment before going down for good.