About previous comment, never mind, it's ok.
About flow, I used dotted brushes to the left part and simple - to right.
I think it will be a bit overloaded, though will try to make something.
Also as I understand, light should go like that:
_________________________
|_______________________ /_
|_______________________/_|
|___________-----/_________|
|______________/__________|

That ------ stripe is light from his right hand since it is light source too.
Also will try to blur some parts a little bit more.

cant find much to criticize
really nicely done
i personally dont like the shadow line on the left

and just one fun and interesting idea is to put the words on the teeth
and did you make the character yourself?

This isn't a simple shadow.
It is a... mmm... let's say it is 2.5D effect (3D, made by 2D) so the signature looked a bit more realistic.
And no, his teeth must be visible, but thanks for creative idea
I don't really know,, how to make this sig - by all sig rules or vica versa.
Maybe I should learn how to make sigs ''by rules'' before creating something unique.
Also no, I won't make my own characters till I learn how to use C4D.
This character is from extremly creative game called de Blob.
You can see some pics here.
I am too conservative to make something like that too .