COOP RPG game that has a wide variety of quests

COOP FPS game with RPG elements

COOP FPS survival game that requires teamwork

Fun hack-and-slash FPS game that requires teamwork

WWII FPS game that requires teamwork

Classic round-based FPS game that requires teamwork

Fun, free, and goofy FPS game that requires teamwork and gives you quite a bit of variety and choices