As a kid I grew up on FPS shooters. Wolfenstein, Doom, Duke Nukem, Quake. All of them were great in their own way. All were milestones in gaming design. But there was a certain game that got trampled on in the FPS race. That game was Blood. And if you play Blood, you will see why no one should ever leave this game under foot!
The level design is amazingly deep. The game is set in an otherworldly version of the 1920s. The games drips with an manic Gothic noir thats engrossing. You'll find yourself on moving trains, sweeping mountaintop hotels, a carnival of the damned, France during WW1, huge cult castles. Not to mention all the horror movie references and nods throughout. It goes on and on. Every level you'll be completely immersed.
The weapons are completely different from your standard fare as well. A voodoo doll, a hairspray can and lighter, a flare gun! Nothing about this game was normal and thats what makes it great. And please don't forget the incredible soundtrack.
Finally, you've got the main character - Caleb. To me he tops Duke Nukem in terms of being a crazy badass. His one liners are off beat and hilarious and you'll find yourself quoting them all the time.
I can't recommend this FPS enough! Get it, enjoy it, and spill some blood!