Made a quick edit of your slime to outline the biggest issue I saw with it. That being the dithering on the shading. The dithering gave him a rougher texture look rather than a shiny surface look.
Hopefully you can see the difference I have made in my edit:
There are a few problems with the shadows still and the light source seems to be inconsistent. I made a wee edit on the shadow of the right-most head, from that I hope you can see how I have shaped his head to be rounder and more pronounced. The last thing I would say about the entire piece is that he seems a little off balance with the left head so far out there. I personally think he would look good with just two heads but whatever.
Keep working at it!