Paintover for you, my bad if it's unwelcome.
Most of the paintover was in the face, eyes and below. Liquify changed (changed...not perfectly fixed) several proportion issues that stood out to me. Tried to keep certain features but still make it more believable/realistic. Also, darker skinned folk tend to have higher contrast in their skin.
If you haven't seen it (it's pretty popular), this tutorial is awesome - the first section on lighting might help you get some better shapes and more confident looking end results: http://androidarts.com/art_tut.htm
Additionally, are you by any chance squinting while you paint at all? I've seen people say it a lot, the whole "squint at your painting" thing, but I'd really recommend against it. Nobody who's looking at it is going to be squinting at it, you need to see what's actually there. The whole squinting thing usually comes from trying to get the overall picture, something you should be focusing on mainly in the real early stages of an image. Better than squinting is looking at a small version of it (or the navigator thumbnail in the corner, in photoshop), which accomplishes the same thing as squinting without getting you in to that bad habit. (I'm not going to say I never blur my vision a bit while painting, but be wary of it and its downsides, is all I'm saying).
It's possible you're not squinting or blurring your vision at all while you work. I only mention it because your visible brush strokes look a lot like mine a few years ago, pretty visible but sort of like a pencil sketch that uses 20 strokes for one short line - a little feathery and lacking confidence. Maybe try to use brushes without any pressure-sensitive opacity on occasion. Using a 100% opacity brush can force you to make sure your strokes are there with purpose, and can be a good exercise from time to time. Also, remember you can often times let shrinking your image help you out a lot in the end. If you're able to paint at 2,000 pixels plus in any given direction, feel free to shrink that shit down to <800-1000 pixels. Easier to see the whole image at once on most monitors anyway, and will help blend some things together for you by hiding brush strokes and the like.
Mostly I've just wanted to say for awhile that I like your rhinocicorn design a lot. But didn't just want to say that.