I'd classify this level into the Maze category... and a very cleverly designed one, at that! I haven't found any of the secrets yet (or gold creatures... or roses...), but my KS skills are very rusty, so that's to be expected. Eretria is probably my favorite area - the tileset, the creatures, and the music just come together so beautifully in it, and remind me of some old DOS games I used to play as a kid. Happy memories. Also many of the caves were extremely well done, a great sense of immersion, vast underground areas. I might have to steal some of these tilesets and solutions for my large level. Also the overall aesthetic aspect was very impressive - choosing tilesets that have some details, but not too much. This made for a very unique visual feeling to almost the whole level. Quite a feat!
Some of the challenging portions of the level felt very jarring to me, such as the fire-spitting torches in the Aquatic Temple, or the wasps in the Afterglow Valley. The former are completely unexpected and kill you right when you're in exploration/wonder mode. That feels bad. The wasps are positioned so that you can get stung right when you enter the screens, let's say if you're jumping from one to another... also very strange to see in such a relaxed area (which I wish was a bit longer). But I think the one thing that somewhat soured the experience for me was the lack of knytts or other creatures you could talk to! I guess this was your intention - to create an unspoiled world devoid of knytt presence - but all that time, I was expecting at least some more signs, writing on the walls, some bit of dialogue maybe from Juni herself, describing what she sees or feels... After a while, the level started feeling uncomfortably empty for me, and I longed to find a screen with at least someone to talk to. Like a couple of hermits, at least, or something to that effect. It was frustrating.
That said, the level is still massively enjoyable, huge, and beautiful. I'm very much looking forward to finding all those collectibles you mention... I hope I can abstain from using the editor...