I really like the direction you're going with this game - it's a good foundation for a bullet hell roguelite with some chill music and fun player/enemy designs. The game as a whole is alright - it functions reasonably well especially given the constraints of a GameJam, but none of the art/music/gameplay elements stood out to me either.
As for gameplay, it felt like +Fire and one or two +Pierces makes the game extremely easy - there's no reason to go with +Atk because the enemies all died in 1-2 hits even with Atk penalties stacked up. Also, because the enemies just move directly towards you at a set speed that you can outrun (except for the shooting ones, whose projectiles made things a little more interesting), they didn't offer much of a challenge. There were also a few oddities I ran into while playing:
1. If you fly around without shooting enemies, it keeps spawning them in and eventually causes the game to stutter a lot and jolt the player/surroundings out of frame repeatedly. If you had a limited count of enemies per wave, or just a maximum enemy spawn cap, this issue could be avoided.
2. I didn't notice any changes to my attacks when getting the Ice Bullet upgrade. What was the intended effect here?
3. The game seems to reset itself to the starting wave after beating wave 14. I'm not sure if this was intended or not, but the immediate game reset was a bit odd. If beating wave 14 gave you a "you win" screen or something similar, that would've probably made this a better transition.
4. When I tried to use my Xbox controller to play this, the A button wasn't mapped. Pressing the D-Pad allowed for movement as normal, and pressing B paused the game, but I was unable to shoot until going back to using my keyboard.
5. When the waves hit double digits, the numbers become misaligned on the screen.
All in all, this was a fun little shooter. I hope this criticism helps as you continue developing your gamemaking skills!