It would have to be left4dead. If you have any enjoyment in shooting large amounts of zombies while working together with your mates and I eman really working together. You go solo in this game, you are dead
Heck even a full team of 4 you might not be getting out of the zombiepocalypse. But you'll die with a smile on your face from the best last moments of life spent with your mates.

Also, 3 of you will love yelling numerous insults at the one guy stupid enough to shoot a witch or get her attention in any manner. ofcourse you'll probably all be dead after he did it.

So you get insult freely while reloading the game

Sure at the moment only the demo is out and you can only play as one of the 4 survivors, but I am already having so much fun with it. When versus mode is released and all the other scenarios...

Oh yeah, come get some,

Hail to the king baby.