Just a little criticism, but when you're doing soft shading, you should try imagining a skull and thinking of how the light hits it giving off shadows. By the ones at the top of this page (Pein & Naruto), they feel too rounded and plump to me and not very realistic. I think that was what you were going for, right? Anyways, you should just try painting in the shadows so it gives it more of a "human" dimension. Its going to feel weird at first, but you'll get used to it. I'm still working on doing that myself.
Your cell shaded ones are great! Nice gallery.
Have you thought about getting a deviantART account to show off your works yet? I'm sure people would love them.
Btw, how do you do those line breaks? I never figured out how to do those.