Interesting concept and beautiful implementation.
Controls are good, but probably it would be ok to use same keys (same row of keys) every round.
About balance of skill game and puzzle game - for me it's just in balance now, you need to think a bit and then make a couple of tries to pass.
Direct control doesn't feel necessary (it even could ruin the atmosphere a bit; for now it's just you and music and it feels just right).
Thank you for the experience, I really enjoyed playing the game.