There are loads of mature-looking 3d games out there. Pok listed quite a lot...just pick what you want and enjoy the game.
My suggested games (based on the mature-looking graphics alright?)
2moons <--- kind of gore-ish at some point..you'll like the blood lol
requiem <--- if you can get a beta key...then COOL! this is super gore!
mutilated zombies and monsters....gothic surroundings...scary-looking character classes.
