Love it! Love everything about it! Great game here, man. Brings me back to the rhythm dungeon mini-game in Rhythm Heaven. I always felt like that needed a revamp. The part that really surprises me, is how great this game is even though it's only a backbone. Looking towards the future I see a lot of great things from this game (If you continue to update it) and you in general.
If you plan to update it, I'd recommend tweaking the timing a little bit. I feel as if I'm pretty good at rhythm games and I can't help but think that sometimes when I fail, I really should've hit the beat. Then again wind up after 1.7x is pretty much becomes impossible haha.
A few ideas I'm just putting out there:
Checkpoints
Level editor/Song import and play
Having to press certain keys on certain beats (maybe a back and forth to simulate a kick-snare sequence?)
One more thing I've thought of is the way you can spam presses/clicks then wait a few beats then do it again. I'm guessing it only checks for spamming if you do it continuously. Perhaps instead of this mechanic you could have a certain number of misclicks per level?
Of course I'm sure there's even more you can think of! Anyways, overall it's a fantastic game and I can't wait to see what you do next! Cheers!