Have you ever tried "Neocron"? Its Sci-Fi themed in a first person view, you fight rats/dogs/bugs in the beginning of your development of your charactor. When you are ready you can go and kill armed mutants in the other parts of the city of Neocron, or you could go out and kill mutants in the large terrain.. mostly the desert. You can't have a mutant as a charactor, but you can fight them. I have not gotten far in the game.. but I got far enough to fight mutants. Go here: http://www.neocron.com