Thanks for the feedback, glad it was enjoyable! We wanted it to feel like an old b movie or lost to time space game.
Regarding performance, there is only so much I can do with the HTML5 version to get it to run better. So many particles/bullets/ships all rendering at once is just not very nice for web games. I have some culling for the ships and bullets, and a lot of tricks to try and get it playable, such as sending all ships to a single rendering image each frame. I think the HTML5 build is simply struggling from the 720p resolution + running at 60 fps.
I'll investigate further post jam to see if I can salvage the performance for this one. However, moving forward, any bullet hell games we make will probably stay download only. It's a constant technical issue I keep running into on making web games.