Wow, that was really fun, and really well done. Fantastic work, that's amazing for 2 weeks. It even has full, well written tutorials! Absolutely amazing, I love it, and I can not praise it enough.
Suggestions:
More music tracks. Ideally one for each character, but at the very least a special track for the final character. The same tune does get old given enough time.
Add a confirmation button before restarting the game. Or disable it once the level is over. I beat a level, clicked away, and accidentally clicked back directly on the restart button.
Add a tooltip to the restart button, I initially read it as an undo button. (Luckily I never tried it like that, but...)
Bugs:
The credits didn't render the names right, like the font was missing the characters for the musician and song, not sure if that's an issue with my machine, the web build, or what.