The contrast between the upper and lower areas was a neat concept. I didn't find the game itself hard, but the controls felt clunky. Some of it was due to visual clarity, like how the same exact looking pillar was something I could stand on in one area but not another, or how I bonked my head on platforms above me that I would normally assume are one-way in most other games (seemingly bonking my head on air due to the platforms not feeling properly marked). I found myself not being able to double jump for seemingly no reason in a lot of scenarios; whether the jump just didn't come out entirely, or I had apparently used it instead of the normal jump right after walking/running off the platform. It likely didn't help that the same sound always plays when you press the button, regardless of if you actually jumped or not. The fact you can (inconsistently) collide with the collectables also often pushed me into the spikes right next to them.
It was fun to speedrun it for a bit, I got <2 minutes after realizing there was a "sprint" button (which to my knowledge is not stated anywhere in the game or on the page?)