Cool game. I really like the boss rounds. Nice Job!
Just a heads up, this wasn't working for me originally so I checked the developer console and it was printing the following error:
error saving game DOMException: Failed to read the 'localStorage' property from 'Window': Access is denied for this document.
I did a quick read on the Mozilla documentation for the Window.localStorage object and it states:
Note that if the user blocks cookies, browsers will probably interpret this as an instruction to prevent the page from persisting data.
After reading this, I enabled cookies and the game worked. This error effectively prevented the game from rendering the crates and enemies (only displayed the player and the background). If this happens to someone else, I would try enabling cookies or using an alternate browser with cookies enabled.