It is my opinion that a shooter is only as interesting as what you are shooting at and what weapon you're using.
I'm not tired of the FPS genre, I'm tired of the "realistic" shooter sub-genre (Call of Duty, Battlefield, et cetera.)
If I want a plain old military assault rifle, I'll go buy one (America, whoo...). Give me a Gravity Gun, a Needler, a Lancer, or a gun that shoots shuriken and lightning.
Instead of generic brown-tinted men who all look and act the same; give me zombies, robots, space aliens, and demons.
In short, I want to play shooters that are imaginative. The coolest enemy you can fight in Call of Duty is an Arab with a rocket launcher. The coolest enemy you can fight in Halo is a thirty-foot tall, purple spider robot that climbs walls, shoots gigantic energy beams out of its face, and is crewed by a half a dozen warhammer-wielding gorrilla-men from another planet.