Not bad man, but you've got to work on when you color it in- your making lines for your shading, you don't want that.
You wan to be able to look at each section and not be able to tell if you shaded sideways or vertically.
That's the one thing I notice wrong
Other than that, looks great, keep it up and you've got nowhere to go but up!!
(okay, that doesn't make much sense in this position, but it got my point across.
)