I think that you should have a look at the base model's proportions as it looks a little off in area, also theres some quite dense lines round the parts the arms join the body, I would try to even these out with the rest of the body as when you go into high poly in mudbox it lets you create even detail (as you dont end up with dense geo patches that you can sculpt into but areas with low Geo that you cant).

also on your mudbox pass I think you went a little overboard with the wrinkles (which I think if your new to a sculpting software everyone does!), also a lot of them seem to go in the wrong directions, try toning it down a little and have a look at refs form say a kimodo dragon for the skin texture ad how the muscles cause the wrinkles and folds.

Youve got the base there so a few tweeks with say a smooth proxy (to get a llok at how it would look in high poly)

Hope this halps and dosent sound harsh, as its not meant to be in any way, just my crit.