This is a cool idea. I think it fits the theme very well.
There were some bugs; I couldn't manage to kill the first goblin guy in the dungeon level, and I couldn't manage to bounce off of another one despite killing him. As a result of this, I could not manage to get to level 4, unfortunately.
Also the game moves pretty slow. I would increase the speed. I would also make it so that holding space isn't necessary; I'd either choose no button at all, or you must press the button right before you bounce.
Overall, you've got a prototype showcasing a cool idea, and it does fine in the graphics & sound department.