Interesting game mechanic!
Challenges:
I found it starts off very easy, but the difficulty spikes pretty quickly. It does not show you clearly why you died, but after a few tries you can see that some enemies take more damage, and move faster than others.
This would be better if it was more obvious, as it is a little frustrating at first.
There are a few levels that look almost identical, maybe 3, 4 and 5?
I think it has some potential as a kind of casual puzzler.