Nice work!

If you think about it, texture is a type of detailed form.  And that's, through my short experience with it, what pixel art is all about.  Form!  It's a combination of shape and color clusters to indicate some depth and turn those clusters into a 3-d image.  

I think in your case here, Mandril is indicating the positioning of your color clusters that elude to where your light source is.  The highlights don't look completely consistent.  There are a lot of good tutorials on form and color theory in the forums that are really good reads.   And don't be afraid to make a thread of any work in progress you might have.  Any criticism you get is from other artists that appreciate the efforts and LOVE great art and just want to see all the amazing pixels that you have hidden within your loins. 

And that being said, I really like your concept.  I can't get enough of character art and it looks like, sans a little polish (which, being honest, we all need to work on from time to time), you're gonna be a great addition to the PJ gallery.  Great job!  

@Mandril Thanks for the critique! : ) What do clusters stand for outside of texture clumps though?

A good start! Some issues with shadows and cluster placement, but overall a pretty nice portrait.