Great game! I love the art, music and general atmosphere but there are a few small things you could improve.
* Perhaps make the music continue even after you die? I die so early and it constantly restarting is a bit annoying. Excellent music though!
* I didn't know that there was a double jump until I played it for a while. Maybe add a small controls sheet where you can mention that double jump and wall jump are possible?
* Atmosphere and art are really great, but it would be nice to have a little less screen shake. You get used to it after playing for a while but it's jarring in the beginning.
* When going fast, the camera lags behind the character meaning it's hard to see what's in front of you. Usually it's a good idea to have the camera slightly ahead of the player so that they can see where they are going.
I also built a game for the weekly game jam, Darkness Defenders. It would mean a lot to me if you played it and gave me some feedback for it!