just super cool and interesting to look at, nice job
it being a little flat was something that struck me too. i can't quite put my finger exactly on it, but it could be some combination of the outlines and lighter shading in some of the areas? some areas pop a little bit less than others, but I don't really think it takes away from the head at all
except maybe in the coils in the back, those bother me a bit.
really though, I like this one a lot. it's really creative and diverse. if it resonates with you and you get the opportunity, maybe you'll consider making the gums a little more fleshy? I feel like that'd augment the feel that's already going on down there, but not sure if it's what you're going for