Great game so far! The atmosphere and unique art style is really something. I played with Mouse + Keyboard. Overall, the controls were good, but the camera rotation was too slow and I didn't like the camera rotate being mapped to 'Q' and 'E'. It made it difficult to move/strafe while rotating the cam at the same time. Maybe just have the mouse handle the rotation instead?
I think a few other people pointed this out, but the boss sfx were too loud and clipping most of the time. It was a little jarring compared to the other sound effects. The rock collision boxes seemed a little too large or I'm just bad at dodging them.
I liked the mood that the music gave off, but there were too many tracks and the instrumentation wasn't that cohesive. You said that you were using royalty-free music at the moment, so that kind of makes sense. I really think having dynamic music layers fading in and out at different moments would really be cool! Are you still looking for a composer? I'm not sure if this is the right place to put this, but I did a couple of mock-up tracks with some video a few days ago and just wanted to share I really liked the organ in the boss music and kept that as part of the instrumentation :)