It's a fun game, and the mechanics are well put together. Nice Job! I do find that the characters fall a bit too fast, and can make it feel out of control.
Also, very minor point, there is no "coyote time" to the edges of platforms, so the characters fall off. If you intend it that way, it all works out. I also know it is a bit difficult to create that.
The idea for the theme isn't all that original - I've seen other games that have the same dual dimension / one can stand on the other. However, good execution. Good job!