The First-Person Shooter genre tends to take itself too seriously. Games like Call of Duty, Battlefield, Halo, and Crysis all have a realistic or serious tone to them. It gets exhausting. People want innovation within the FPS genre but I think part of that is diversifying the genre through simple additions like humor. A game like Gotham City Imposters is on the right track.
Here are five comedic–and slightly unrealistic–ways the FPS genre can develop variety.