The contours of the back, shoulders, and jaw look really good. I'm not the most experienced with accurately rendering skin, and it might just be a stylistic choice, but the sharp highlights give the impression of a very high sheen that you don't get unless the skin is wet/greasy. I should try my hand at this sort of thing-- there's a lot of pliable muscle and fat in the body that I've thus far kind of ignored like a gremlin XD.