It is not bad, but, if i may offer some critics?
Okay i try not to be too hard.
Take another brush for the ground, you see, it has those hard inklines and those airbrushed highlights just don't work, it looks puffy or blown up, wich it probably isn't.
The light in this piece is very dim, so the hard reflections on battle cat make no sense. Also on the metal on ram man to is too bright for the sourrounding light and he-mans bracer wich is even not on the sunny side if we check the rest of his lighting.
The shadows on he-Man look more like dirt, i would suggest you use another layerstyle and mainly not black as shadowcolor on skin tones. Use a brown or whatever skin you need to darken.
Overall, by this light i would have given it all a blue tint, like a night scene.
For the light in grayskull, if you use layers, wich i guess you do, put a new layer on top of the inking, and use a light yellow and the airbrush brush you used on the ground for the glow of the light, that might do it. If you use photoshop, put the layer on linear dodge, and the opacity of the brush very low, the lighter the color on this layer the more exposure it gets. Be careful with that.
But for the coloring over all i would suggest, don't use layerstyles at all. Maybe you don't and all that follows are words for nothing
For the skin you lay your flat color in the inks (seperate layer of course), than you have your hsb palette thing open and when placing the shadows put the skin color in your brush, and then correct the lightness with that little levers. You will learn more about how color reacts on one another, even if it is digital.
There is a fun example.
Make a new document in wide format, make one half white and the other a 50 percent gray. Then, pick a skin color, or a light pink. Then a nice brush like crayon or something, at least one with a hard edge, and paint with full opacity some dots in the middle of that white surface. now, do the same with the same color on the gray side. You will see, that the dot on the white side looks way darker than on the gray side.
A reason never to paint on a white canvas
Anyways, you have well better control over your colors by using the lever on the brightness or Saturation, depends on what color you are looking for.
And again, don't use those puffy airbrush brushes if you don't have an airbrush image or a very puffy fluffy cloud or something. Or a gradient made by hand...
For these kind of artworks, harder brushes work better. The softness in the hightlights comes from the selections. There you feather your selection with some pixel, depends on how big your image is. And then you can go over there with a hard brush and it makes almost no difference (depends again on the options you use, but normally it should work fine).
And one last thing, it comes from a more traditional painting area, if you lay color in the background, let it fade out. not into gray, but check you light on the hill of grayskull, that thing lies in total darkness and the road there is brightly lit. That is unnatural of course, there you could have, and probably should have made a gradient, not with the tool, but with the darker color. The airbrush would come in handy here... load it with a very dark version of the flat color, and go from up hill down to your guys and get ever so slightly lighter. But is should not be black up hill, just a darker ground color. Why? Well, you have atmosphere in the real world, little particles that "cloud" the view. Fog is a nice example, it is very thick, but if you stand on the ground and look for an object that is very far away, it looses is details and saturation of color. The thing with paintings is, what is far away is less saturated than the foreground. The colors are much brighter and leads the eye of the viewer to the main thing, the guys in the front. But that is probably too far...
Hope i could give you some ideas.
First off thanks for the honest critiques and a lot of it does help.
still a couple of things
1. I don't use layerstyles at all, I could even send you the actual psd file so you can see that I don't
2. Didn't use black at all on any of the skin tones
3. I did originally have a blue tint over the picture as I am aware that is a good way of doing night scenes but for some reason I just didn't like it at all, it's a personal thing. Honestly I have never liked blue tints for night time scenes in comics, yes that may be weird to hear as the blue is obviously there for a reason but in everything I have read I have always found it to be both distracting and slightly unpleasant to look at. Still again it is just a personal thing.
still when I get round to fixing this pic in the next week or so I will re-add the blue tint