#5 Portal series

Both Portal games have managed to spawn a cult following thanks to their intuitive puzzles, cleverly-written characters, and the genuinely fascinating Aperture Science Labs, in which both games take place.

Not strictly a "shooter" and much more of a first person puzzle game with a Portal Gun, Portal (and its sequel) nonetheless draws heavy inspiration from its FPS predecessors. Considering the fact that the Portal Gun is fired, I decided it'd be wrong not to count it among the greats.