Mark - since you asked for critique, I will point out one minor thing that occurred to me. As I said earlier, and everyone else also says, this is superb. My only observation that may help is on the photo that is face on - when front viewing, the highlights on either side of his nose look a little bit like light flesh lines leading to the inner corrners of his eyes (sort of an upside down "V"). These might benefit from being toned down just a little as they proceed toward the eyes. Just a thought.
Cheers
Colin