Visually and feelings-wise, this was great! The idea and setting were so cool and it was a neat idea to use public domain art. You definitely put those artworks together well into a cohesive whole.
It's also very impressive you made this all by yourself!
During the collecting phase, I think that the circle for collecting a flower, especially vertically, should be a bit bigger. I had quite a few frustrating near-misses.
And during the fireworks phase, my frame rate dipped to like 5fps or so whenever a firework particle system was playing. And that then affected my ability to play the rhythm game for the next one so I had quite a lot of failures due to the laggy frames from the particle effects.