I like the concept of your game! The skybox is cool, and the UI is awesome. I think you have a good foundation here.
Some feedback:
Spamming bullets: This can make the game too easy and repetitive. You could consider limiting the number of bullets that can be on the screen at once, or making the bullets do less damage if they are fired too quickly.
Simplistic gameplay: This is not necessarily a bad thing, but it could be improved by adding more variety to the enemies or the levels. You could also consider adding some power-ups or special abilities that would give the player more options.
No sound effects: This can make the game feel a bit empty and lifeless. Adding some sound effects would help to improve the overall immersion.
Destroy particles that are too large: This would help to keep the screen from getting cluttered and make it easier to see what is going on.
Cool skybox: The skybox is a nice touch and helps to set the scene.
The least challenging game I played this jam: This could be improved by making the enemies more difficult or by adding some more challenging levels.
No reason to not hold the shoot button: You could consider making the shoot button automatic, as is the case in most other bullet hell games. This would free up the player's hands to focus on dodging enemy fire or adding some ammo.
Awesome UI: The UI is well-designed and easy to use.
Y position of some objects is offset wrongly: This can make it difficult to hit some enemies or objects. You could consider adjusting the y position of these objects so that they are easier to hit.
Overall, I think the game has some potential, but it could be improved with some additional work. I hope this feedback is helpful!