This is definitely a unique concept, the enemy and level types are well thought-out, and it's a great example of what can be reasonably done in a game jam's timeframe.
My only real complaint is that on the levels with the 2 buttons, if you don't -immediately- react, or you do, but you accidentally recoil yourself off the button, you get stuck in a state where it's impossible to stay on the button long enough, at which point you can could have 7 hearts saved up and still basically auto-lose. I would suggest resetting the level if you take a hit while the monsters are still shielded (so you still lose a life, but it's not an instant game over).