I like this drawing, but I am strongly against the black shadows.
I know this is a classic comic-book effect, but it works best for really strong core-shadows, and even so, they're very rarely used in detailed illustrations like the comic book's cover. They're there to save time, really.
If it's not too late, leave the black shadow shapes out completely - do them justice in rendering. Shadows are delicious to render, picking up the ambient light's color, and subject to all sorts of effects like subsurface scattering, bounce light, and ambient occlusion. Don't do your picture a dirty by making the shadows black.