Thanks for the feedback, I'm glad to hear you enjoyed the game! To comment on a few of these points:
The enemies used to throw neon shurikens, but it made the game confusing and visually cluttered to I took it back down to just gray.
I wanted a melee attack, but I sort of ran out of time and it just didn't really end up happening.
Originally, the waves started on their own, but I felt like it was better for pacing to give the player a moment to catch their breath and look around for upgrades between the waves, especially the later ones.
That's a good tip for the music, I'll keep that in mind for my next game!