This was the most soothing game I've played thus far. I was getting some digital clipping as the complexity of the soundscape opened up: if you revisit this idea, make sure to watch the volume of your audio sources as they all turn on, and be careful about balancing them.
But with that said, I think you could definitely make more levels for this game with different challenges, maybe have a "par" for each one so the player has an idea of how many shots they should be trying to take (though don't punish them for going over).
All in all, great game and excellent music. Keep up the good work!