Whenever you're doing a drawing in color, you have to be conscious of which colors you're choosing and for what. Every picture needs to have some sort of color scheme; otherwise, it looks scrambled and inconsistent. Here's a color theory tutorial that I think is pretty good(I used to have a better one, but stupid me lost the link).
My other broad comment is that you need to work on your anatomy
Now for individual critiques.
The illumination coming from the lighter is far too intense for how bright the rest of the picture is. It's also very monochromatic. The sky could also use some more detail and variation in color.
Picture 4 and picture 6:
I recommend adding in objects into the background instead of just having it be all sky. Also, I noticed that you said that you gave him two sets of hair because you wanted to show that he was jumping between them quickly, but you really can't show that in a still image without it looking strange. You have to pick one or the other, or make it a .gif. Additionally, make sure you pick a direction of light.
Similar to picture 1, remember that the brighter your background light is, the less intense the glow from a secondary light source is going to be. So, I suggest either toning down the glare from the fire or coloring in the background so that it's a dark setting.
If you're going to have a reflection on the armor, then it looks out of place if you don't have shading on the rest of the body that reflects that same light source.
Picture 14 (the last picture):
I agree with Fifty-50. I'll also say that your direction of light isn't consistent. On certain highlights, it's coming from above, but on other it's coming from the left. Additionally, everything looks too geometrical for something 3D. It's okay to cartoon like that, but once you start going into something that should look more realistic, it's not flattering.