Well, in recent history FPS games have become cookie cutter "COD at heart" games, what with the same gameplay, mechanics, etc. Last good recent FPS was the COD 4, because it was fresh, at the time, and it actually needed a coherent story that didn't rely on explosions or a built in fan base to sell. *coughMW2cough*
But for originality, at least, something different, I'd recommend the STALKER series. Yes, they're buggy, but even without patches and mods up the wazoo, it's immersive, tense, and honestly fun. Also helps that it's open world.
Another one I'd recommend is Deus Ex. Might sound like the same old argument, but no game has ever managed to mix a multi-path FPS with RPG mechanics and a brilliant, if crazy, story.
Just saying.