I played the game a bit for now(since I will have to play another game then I need to sleep), and overall it is looking very enjoyable. Really loved your use of the color theme restrictions for this jam---you made a really well polished minimalistic visual layout!!!
I haven't made a bullet hell game specifically so I don't know the restrictions to the code, but here's a bit of thoughts:
-The regular enemies usually attacks in a similar manner. For a small fix, I think reversing the rotation of some enemies & bullets could be interesting.
-From the levels I played, the enemies usually spawn twice from the same layout. I see some differences in the bullets, but it could be interesting to move the enemies ever so slightly/switch up the times when their bullets are shot a bit to add variation between waves.
These are just some of my opinions, as I said, I don't know how hard it is to implement these; however, the game looks amazing and is really enjoyable!