Couldn't get past the Lighting door in level 1. The first Lighting key seems impossible to pick up. You can also easily softlock yourself a lot of the TImes. And I don't really see any nonlinearity. You could go pick the left key up first, but then you'd have to just completely backtrack to get the right key, and then backtrack again into the left. Theres no looping around or anything. Theres an Area with a few Stars in it behind a wooden Plank, but thats only openable from one side as I see it, so I couldn't get there. Music gets annoying after a while, maybe it changes on different Levels, but as I said, I was stuck right in level 1.
From what I've seen scanning through the Comments and watching that YT Video, its me being retarded, not the first level being impossible. Should've probably jumped on the Barrel(?) But immediately got it stuck under the ramp on the left and couldn't get it back out. I lost interest after that. Its just not my kind of Game. Sorry.