While it might not be the official ESRB classification, everyone knows what to expect when they hear, "R-rated FPS game." Oh yeah, here come pitch-black themes, splashes of body horror, maybe a serial killer or two, and a tsunami of blood. M-rated shooters are a dime-a-dozen, but that doesn't mean they all qualify as R-rated. They need to offer something more than just gore, as awesome as that can be.
