some really nice work there.

Improvements : -

apart from the mouth I think the chin needs some tweaking as it has very little shape

the neck - If he was to have shoulder muscles like that they would be more defined - just look at some body builder pics and you`ll see. If your going for a more natraul look then the side of the neck would not look like that and then needs some tweaking. At the mo your stuck in the middle.