To the point, this was a excellent game! The visuals are clean and clear, the sounds are on point (love the sound when hitting an enemy), and the controls, while simple, are very responsive and intuitive! I also love how you added not just power-ups between levels, but a choice of power-up! That adds just that little extra!
For the core of the game, there really isn’t anything I can think to suggest that would improve the game. Mostly it would be stuff that would make my game easier, lol! I suppose, outside of the boss, I think it might have been cool if, for the “persistent bullets”, I could have control of their orbital radii to some degree.
At the boss… beyond the visual bug, it is definitely too long with the abilities given. Even if the “special” attack would regenerate a shot every 5 to 10 seconds, or after every 10 or 20 enemies destroyed, I think that would make the fight go a little faster. Also, it felt like, after the visual glitch occurred, all of the enemies just kinda stopped attacking. I lost all sense of threat in the end… which is definitely not something you want to have happen in your boss fight!
Over all, as I said, this is an excellent game and very well done!!