I think you should try to go even harder on the rim light. It'll probably help define the shapes of his upper body even more.
It also seems that you're going for a sort of oozy quality for the melted part of him. Consider replicating a little of what you can see on this artwork from Hearthstone. Your style is very different, so I don't think it's smart to try and copy it, but I think studying how they've used light can be beneficial in defining shapes and textures, especially on his lower body, where the values are very close to each other.
I think what I like the most is his expression, pose and the colour palette surrounding his face. The red blue and red on his upper body works really well together. I also think the transition from torso to his lower body is especially good, you've definitely nailed the, sort of, melting strings, between his body parts. Good job.