You post a lot.

Also, the gradient effect and contrast seems a bit severe. Try dumbing down a bit of the brightness and saturation. :)

Hmmm, not bad. I do have some contstructive criticism (and tips), so bear with me ;) :

1: try to avoid using fully desaturated colors in skins (black, gray, white, etc. Otherwise known as "perfect grays") instead subsititute desaturated colors for perfect grays. I do that with every one of my skins when I'm trying to simulate gray or black or white. My Slenderman skin is a good example of that. (It's not bad to use black and white sparingly, though. ;)

2: Usually when I darken colors for the shading, I decrease the saturation. Why? Because light is made up of color (Wiki "Visible Spectrum". It's an interesting read), thus making it so that the less light an object absorbs, it in turn absorbs less color.
I kind of explain my method of desaturated colors and saturated colors in this picture tutorialà here. Also, sometimes i actually increase the saturation as the colors get brighter. I differentiate between desaturated and saturated highlights whenever I want the skin to feel realistic or cartoony.

3: Hue shift the colors. Hue shifting (in a nutshell) is shifting the colors for each of the hues in your skins/pixel art/drawings/etc. The_soup and Levaunt both have great explanations regarding hue shifting in their blogs

Levaunt's explanation

The_soup's explanation

Happy Skinning!