Interesting concept, great art and music!
However, as others have commented, it broke my brain to have the keys laying horizontally on the keyboard but vertically on screen, it took a while to get used to and was mildly frustrating, especially considering that the difficulty ramps up quite fast and that you have to wait a while for each try! For short JAM games like this I think having very low retry delay is a good idea :)
Also, for some reason the calibration didn’t seem to work well for me, I tried it several times and it always gave me a delay of about 120ms, however the notes were really out of sync with that delay, I manually set it to 0ms and it was much better.
In any case, nice job putting this together!
~kiko