The illustration itself is fine. Nice combination of your own flair and the look of the MLP:FIM style. To me, the biggest flaw in this particular piece is in the composition. You need to crop the image more closely, drawing the attention in to the portrait more. At the moment it looks too much like a head floating in a large sea of nothing. The artwork loses impact because of it.
The colors and the illustration are both eye catching--in fact, the colors are wonderfully vibrant--but the scale makes the drawing appear small. For portraits I've heard it said that you should get close, then get closer--and then get closer; I agree with that concept, and think that it would benefit this drawing a great deal. Filling the page with the illustration will make it pop much more.
On a more personal opinion note: Dash looks a little soft, but that has nothing to do with the quality of the piece.