his mouth should be a tad bit more wider, but looking good there..
Allthough there's something about the chin/mouth area that bugs me, and it's not just the mouth.. But can't really pinpoint it :/
Edit: Think I got a few things.
1) The lower lip should be a tad flattend at the bottom.. your lower-lip goes like this: \/ , while it should be more like \__/, know what I mean?
2) Mel gibson had a real flat eyebrow line, you got more of a ^-^.. try to flatten that out and make him stop staring like that
He has pretty small eyes if you ask me