Is it drawn with brushes and a mouse? It might be this crappy low res screen I have to use right now but the lines look very messy.
You need to define your light source, the shadows are going in a bunch of different directions. Their opacity all looks good besides the teeth, but that shadow doesn't look right, needs tweeking. The shadow at the top of the body should curving the opposite way. Doesn't need anymore colors, keep it simple like that.
Otherwise I like it, reminds me of aqua team hunger force.