I'm happy you're mostly enjoying the game, and don't worry we're all trying to play a few more games before the end of the jam ;)
I'll need to work on the grey screen of death in the browser version, you indeed can't save while levelling-up because I put the save option only in the menu with the characters but not in the main menu with the settings options (for no particular reason).
We always appreciate comments about our music since it's the part we struggle the most with so thanks for that as well.
Thanks for playing and the detailed feedback!