Extremely challenging and has the coolest bullet patterns I have seen (especially the 3D cube and slash effects in W4)! Like other people said, the audio is hard to listen to, as it feels compressed too much. I managed to get to the 4th world final boss, but it crashed for me. Overall fun and challenging!
Viewing post in 3BUTTERF.EXE jam comments
i'm aware of the crash, it's been fixed in the post-jam version: https://verysoftwares.itch.io/3butterfexe
if you still want to see the final boss, you don't have to play all stages again - just select Practice mode and go to boss4.