It's really fun once you get a feel for it. Of course as you already know audio/music would be amazing. I think what would help a lot is less boulders and more of some other kind of enemy type. For me I felt the optimal strategy was to build up speed strafe jumping, and If I did this correctly the boulders could be completely ignored. However, when moving slowly they are nearly impossible to avoid, so maybe an enemy that shoots slower moving projectiles to make circle strafing more difficult and less boulders to make some moments of respite a possibility (just my suggestion, I'm sure there are other ways to balance as well).
Also, I feel like a got a pretty good score so I want to show off :)