I like the concept behind the game, and I think you're well on your way to have a finished product in your hands; once you've finished adding assets and implementing menus, I think the only stuff that's really missing is a big round of juicing, for which I recommend using Super Hexagon as a reference (to be clear, I do like your choice of SFXs and animations so far, I just think you need to add more, because this kind of geometric style has a harder time carrying its own weight).
As for the gameplay, allow using Z/X to fire white/black bullets, and I feel like you should be able to fire at a slightly higher rate when you don't hold a button. Lastly you could consider dividing up enemies in waves, with a wave counter, to give the player the occasional breather ( you could further expand on this by making some levels where the player wins after x waves, and treat your current game as an endless mode).