I like the concept, but in the current state it is to easy. This could be a puzzler, if every level was possible to beat with all hearts left. Then the player could replay levels to try to get the highest rating (all hearts left). But you might need some more elements like walls or obstacles, that one kind of enemy can pass.
Some in game advice how to play would have been nice.
This is a well done game with potential for more. Keep going.