The shading and shadows arent entirley correct. They start off rather smooth, then go into hyper shading (which is somewhat rough looking). Try to make the shadows look cleaner, and more sold. And try to work the texture on the left half of the image a lot more. Oh, and i dont know if youve noticed this, but the light source seems to be bending around the right side of the skull, its lighting on top and on the bottem.

Im not going to mention everything that is wrong with the lue worm thing, so just know that the shadows are just plain wrong on it...

Looks pretty sweet, just try to unify the light source, and smooth your shading a bit, and it will look far more epic.