Hello, this is my first time doing a critique, so be prepared for fails(s) in this one.
First of all, I had seen many artworks with a similar style as this. (Try out: MLP: Two Sides of [insert MLP character here]. Not that I'm trying to be mean but, the coloring and shading needs a LIITLE more practice. Try using the Burn tool thingy in GIMP and change the opacity to 90 and gently apply the shading, oh, and try using a font when applying text
Thank you for reading my VERY FIRST critique. Hope to see you improve! (In a positive way, of course..)