Recs.
Updated
Left 4 Dead 2 is a co-op first person shooter from Valve. The game features four survivors, each played by an online or offline player (or sometimes just bots), whose role is to cooperate and try to make it through an assortment of campaigns, each with different game modes. This is done through with the help of a variety of weapons.
SpecsUpdate
Pros
Pro Turn the gameplay upside down by hunting the hunters in a unique co-op mode where you play as the zombies
Left 4 Dead 2 features a co-op versus mode that pits two teams against one another. One takes on the role of survivors, which is very similar to the normal campaign. The other team, however, plays as the infected, opening up a whole new play style and set of strategies.
Pro Invigorating cooperation based survival dynamic
Left 4 Dead 2 requires players on the same team to cooperate to survive. This makes for an interesting dynamic for teammates, as it will be increasingly difficult to make it through a level if any one player decides to go off on their own.