I thought a bit about the overall drawing, and in my opinion at the moment it seems more a technique exercise than an illustration. What I mean is that it's technically great with shadows, colors and contrasts that work well together, but the subject itself is lacking something. Leaving apart drawing techniques, what I see is a generic face without expression in a space where nothing is really happening. Nothing that indicates who the guy is, where he is, how he is. The painting needs something to catch the eye of the viewer: some clothing, some kind of jewel, some elements in the bg, a particular facial expression or even just a glow in the eyes.
Not necessarily a bad thing if you were going for a generic drawing to warm up your skills after a pause, but at this stage I feel its overall direction is still not defined.