Very fun, the atmosphere and tone were great and fit the art and sound perfectly.
Controls were a little finnicky, lots of deaths because I hit the key for just a fraction of a second too long. It was starting to get just a hair too repetitive toward the end, if you were to continue working on this game I'd suggest introducing a new mechanic right around the 4th level after the player feels like they've learned the jumping and all that.
The level design was perfect for the first handful of levels, I was taught new strategies exactly as I needed them and then those were later incorporated into later levels.
I found myself very invested, tried the farthest level (I could get to) quite a few times before giving up because I couldn't figure out the way forward.