Okay, so some of the proportions seem a bit off, which I show fixed in this picture.
Beyond that, there are some of those subtle shapes in the muscles (which I didn't paint over, since I'm still getting used to.) that aren't quite shown. Tricky places like the legs and knees and some of the back. You did pretty well on your own, so I don't think it will take much work to make it look just right. Get some decent reference and I don't think you'll have much trouble 
