I looked into the game a little further than the surface gimmick, but I was limited in how much I could find because even if you know it's there to look for, it's still hard. And it looks like most other players who've left reviews haven't looked even that deep.
I feel like adding a mechanic to make it possible for the player to slide down a 1-block size gap if they're near the center by pressing down (as well as making the browser screen not scroll if the player presses arrow keys while playing) or something would help at least with level 1, because otherwise it's annoying (not challenging fun) to do it. With later levels I've only found some but definitely not all of the stuff to find, so you would know better than me whether there are other mechanics that might've been lurking in the back of your mind as potentially being a similar kind of issue.
Maybe it's meant to be hard, but it's tough for a dev to judge difficulty when they've designed the secrets and spent hours playtesting their game compared to a player coming in as a blank slate, and it feels like this one might have overshot which I've definitely been guilty of doing in my own games.