nice, they look very good. i recommend using gimp though, it will get rid of that "flat" effect. i am not very good at heads, but i just started experimenting with 'shading' and i figured i might as well give u an advantage. use an airbrush under certain edges to make it look more 3d.
i really am not very good though, so i cant show u any epic examples, i would look at sum of darkjaks stuff though, hes really good