However, Doom and Quake 2/4 are virtually the same to me. Quake 1: techno-fantasy (Lovecraftian monsters in medieval castles fought with modern day or futuristic weaponry) Wolfenstein: World War II and its derivatives
However, they also have their distinct styles: Now, all of those basically come down to the same thing: shoot the bad guys. Rage (technically not a series yet, but a sequel is planned for an unspecified future) Id has produced (or supervised) a number of FPS games over the years, all of which come from one of those series:
