The music is the real start of the show. Great, great stuff, I'm so in love with it!
Yeah, as others have stated - it's quite simple, but the music ties it nicely, especially the song progression. The upgrades seem a bit underwhelming, some are good, some are trash (like the regen one). I like the fact that you're preventing the player from inifinitely kiting and spawn the shooter enemies.
And I got filtered by the boss. Great stuff, please keep it up!