You've done an amazing job with the game, especially in such a short amount of time! The other comments are right, it really does feel pretty polished.
I have a small piece of feedback that I hope you will find useful! It's not major, just small things I noticed. I think it would be helpful if the camera moved up to the relevant area when you were entering a new zone, so that you can see where you're going and so you can see and anticipate enemies. Similarly, since the runes in the first boss room were on the far northern wall, it actually took me quite a bit to figure out what you were supposed to do, and I was going off entirely from the sounds the buttons made, thinking that was the only indication.
I really like how it had an element of genuine challenge to it and took a few tries to understand and beat.