The UI is very polished! I also appreciate the remappable controls, though some buttons use Enter and some use Z.
As for the gameplay, I think the time-to-kill of the basic enemies is a bit too long, given that they often spawn in a group. Also, they all shoot at the same time, and each shoots two bullets at different speeds, which creates a blanket of bullets that is hard to dodge, especially when cornered by their movement.
Talking about movement, I dislike how the enemies are invulnerable when they move in at high speeds. Most of the time, I cannot outrun the enemies spawning offscreen and get crushed. I think the formations are very cool, but maybe reduce their speed or indicate their movement before they appear.
Finally, the loadouts are a cool concept, though I can't help but feel that the game is currently balanced around the yellow loadout. The purple loadout has abusable missiles (holding Z and occasionally pressing X), but no shooting backwards is a game-breaking disadvantage. The fish... it has laggy hit detection and hitsounds. It would be viable if it could knock back bullets like a baseball bat. But currently, with the frequency and density of bullet spawns, melee is not playable.
Overall, it is a fun game to play!