It's mostly the cropping that bugs me. When seeing someone's profile, it's always nice to leave more breathing room (in front of the face). So in this case, I think if you'd crop it square and just remove what's behind his head, the shot would benefit.
And I almost can see a little green tint at the base of his hair, so a little color correction for shadows and midtones could help too.
But the expression is really nice and I think on that you've depressed the shutter just at the exact right time.