When I painted my own Ryu years ago this was one of my refs/inspirations. Ultimately, I changed quite a bit because to get to fit properly as a sprite, but still be muscularly ripped and have cool wrinkles.
I remember I saw this drawing in someone's avatar in a website a long time ago. Looking at it from a bigger resolution it's easy to know why he chose it. It looks terrific, for a lack of a better word. It'd be unfair to describe only specific parts that I liked, as I liked it as a whole, but if I had to choose, the energy ball definitely. Simply love it!