It's really unfortunate you don't want it on mobile... The setup and controls are a perfect fit for touchscreen, since technically you don't really need WASD to move. It would be awesome if you reconsidered it :)
As for the polish suggestions, here's what I think should be added/modified:
- Death animations. Right now enemies just become stiff and change color when they die. It would be nice to add some kind of animation to it.
- Gems. For some reason gem images seem a bit out of place. IMO they're too big and have too much detail for such a simplistic artstyle. I think you should look into slightly modifying their look.
- Punch sounds. The sounds you make when you punch through something are a bit bland for such an awesome action. They should have more oomph to it, be more snappy.
- Cutting through enemies. That speaks for itself. Would be cool if you could kill enemies not just by dropping stuff on them, but by punching through them as well.
- Click spam protection. Right now, it's pretty easy to pass most levels by just spamming leftclick everywhere. You can't die as long as you don't punch into an enemy. I don't think it was intended that way, which is why I believe that you should either implement some sort of punch limit (cooldown for example) or slightly tweak some levels to make it harder to clickspam them.
- Player death stutter. Sometimes the game stutters when your character dies. You probably know about this already, but still thought I should mention it.
That's about all I can think of off the top of my head. The game is really good as it is, but I think these little changes will make it even better :)