I had a lot of fun coming up with this list, of course there will inevitably be a game that should have been included on it that somehow slipped my mind. But for now, I can live in the fantasy that I covered all the bases with this list. Keep in mind that I left MOBAs and games like Black Ops 2 off the list intentionally, while they defiantly have some great cooperative offering their primary focus is a more competitive space.
#20 - Shoot Many Robots
#19 - Renegade Ops
#18 - War in the North
#17 - Bulletstorm
#16 - Dead Island
#15 - Dawn of War 2
#14 - Garry’s Mod
#13 - Magicka
#12 - Borderlands 2
#11 - Torchlight 2
#10 - Orcs Must Die 2
#9 - Killing Floor
#8 - PAYDAY: The Heist
#7 - Resident Evil 5
#6 - Saints Row 3
#5 - Trine 2
#4 - Terraria
#3 - Dungeon Defenders
#2 - Portal 2
#1 - Left 4 Dead 2
