Well, as I've said before, I am my own worst critic. In all honesty, I personally don't think that my coloring skills are all that great. Relining and cuting in colors is childs play compared to shading and shadowing....both of which I'm not very good at, down right horrible in fact.
It's not too bad. I think it could use some more shading though, as it's a little difficult to tell from what direction the light source is. I can kinda see it coming from behind, and from the front. And some of your lines are drowned out, or are competing with your colors.
I can show you another way to color if you like. I'm doing a shot this Friday on coloring images.