What an incredible, grueling little game (in the most affectionate way possible). Honestly surprised I seem to be alone in the camp of "wow this game is kind of miserable" (but again, in a good way). Part of it is probably that I suffered through the first like, 2/3rds without it being fullscreen because I couldn't figure out how, until I realized I needed to do it manually via my browser options - when you said to make it fullscreen, I kind of expected some kind of in-game ui function to allow me to fullscreen it.
I do wish the ending was a little more satisfying, though. It felt like it was leading up to something, narratively, especially with the "that's why we're here", "we've broken your legs", and "it's for your own good" type lines, and then the ending sort of didn't have any kind of reveal aside from "well, you can fall down or climb down but this is all there is". Especially after struggling through to finishing instead of giving up many, many times, it felt like Some Kind of payoff was earned, but there wasn't anything to be found. Even something as simple as "oh, you thought you were through? that's a shame, we'll do this as many times as it takes" and teleporting you back to the beginning or something would feel more in line with the narrative lead-up.
The gameplay is very fluid and feels great, even the parts that are miserable and frustrating end up being very satisfying when you finally figure out a way to get through them. I was also constantly getting myself stuck places, often because I'd try going a different way than the arrows directed because I saw there was still open space and thought maybe there'd be an easter egg or something in that direction since it was like, Conspiciously Open despite not being where the arrows wanted me to go. The first few times that happened I ended up having to restart, but eventually I did learn how to get myself unstuck with some success. That being said, the arrows were very helpful in general, when I wasn't being a pain in my own ass.
Great work! Easily one of my favourites so far. I hope you'll keep working on this, would love to see how far you could take it.