I love how you drew Fluttershy, as well as the human version. The hi-lights on the cheeks and nose seem to exaggerate the surrounding colors, and give her that famous look of innocence. I also love how well the wings turned out; they look delicate and beautiful, even when still, and give her that further look of shyness with them seeming to be about to curl around her.
However, (and I'm not saying this to be prude), but her... breasts seem to be different sizes, making her disproportional. On that note, it also seems like the shoulder turned out too big, but not staggeringly so.
It also seems like you stopped putting details into the hair halfway through, and although this could help accentuate the shadowing and may be intentionally made, it is of my opinion that it seems out place when everything else is detailed. (I am talking about the human Fluttershy)
But other than that, this is a beautiful piece and I will always enjoy your art. Sorry if anything came off as rude, but I just felt like sharing a critique not only to help, but also because from what I can see, no one has made any as of yet.
I'm starting to ramble, so I'm going to stop typing now.