I'm a complete n00b, and a lousy artist, but I'll give my opinion:  I think it looks really cool.  I love the face and the hair. Good job.

Some little things that bother me: 

The shadow on the left cheek looks a bit off to me.
That one red pixel in the hair in the lower right really stands out.
Your face is the same color as the background...weird!  But it looks like you are using only 3 colors, so there might not be much you can do about that.
The more I stare at it, the red shading on the yellow skin looks more and more awkward.