First if all I think you did an amazing job, with the shading... eyes... It's all awesome! Funny that my favorite is Pinkie Pie, so that makes me love this more! Though I really think that you could've done a better job on the background, because pink is one of those background colors used too much. If I could change one thing about this picture, that would be NOTHING! It is too awesome for the words... Really, I do think that the technique you used is very unique, you should join Hasbro and draw the ponies! No lie, that's how awesome you are!
This piece is very beautiful and fun!!!! I think that pinkie is in her true element in this picture, and I love how you enhanced the size of her mane and tail, which makes pinkie all the better. the only thing is the fact that Pinkie is well, pink and that the background is also pink, the color pink starts to get overused. The artwork is still very beautiful, but I feel that having a blue or yellow background would suit this piece a little better, and with blue and yellow it would bring out the color in her eyes and still have pinkie pop ad be the center of attention. Other than that I would not change a thing. The art is amazing and it will definitely be in my favorites! I LOVE IT SO MUCH!!!