1. The drawing is pretty good, but I find it lacking in different techniques, you could use more antialiasing and definitely a bit of dithering to avoid pillow-shading.
2. The palette is really dull, because I suppose you have created it by moving the color hud horizontally, so you might want to try other colours to do the purple´s shadows. Personally I would carry it to reds in the darker colours and I would change the bright purple for a blueish tone.
3. This is more a personal thing, but I would get rid of the purple background to fuse it with the black part of the figure.