I think this looks really nice; the hazy, luminous quality to the highlights is a good touch. My only issue is that some of the highlighted areas feel like they would actually be in shadow, or might be shaped a bit differently based on the shapes that make up the head. For the quickest touchup, I'd temporarily add a layer with an arrow showing the intended direction of the imagined light source, focusing on which parts of the head would theoretically block that line if this bust were a physical, three-dimensional object.

But that's really just a nitpick. Maybe some highlights are out of place, maybe I'm imagining it, but more importantly it reads clearly as a shiny, goopy surface reflecting light. Good stuff.