What a wonderful, beautiful experience.
On an aesthetic level, the tileset is absolutely beautiful--the strong contrast between the verdant foreground and the dark purple background is simply gorgeous, and although this color combination by itself could be forbidding, the addition of the warm orange flowers brings a touch of warmth that makes everything feel so lively, and the contrast between the purple deep exterior background and the darker green interior background creates a nice sense of space. It's a wonderfully comfortable place to explore and inhabit.
The level design is stunning too--playing through it and secret hunting, it struck me how open the space was and how many different paths you could take through the environment. It's a joy to navigate around and learn the different pathways you can take and how they interconnect as you fall. The navigation puzzle, where you have to figure out how to get to the stone block from which you jump to get the secret detector, was one of my favorite moments of the level. It also struck me how natural the contours of the environment seemed. You have to make a lot of jumps, including some tricky ones (like riding the updrafts to get to the uppermost key), but never did I feel as if I was obviously being tested. I really enjoyed that feeling. You're right to call your level a "playground", because that's really what it feels like. It's a static set of monkey bars to fiddle around on, as challenging or easy as you want to make it, and I really enjoy that feeling.
Lastly, I want to compliment your choice of music. Fits the scene very well, and I miiight have left it open in the background for a while just to enjoy the music + waterfall noises ^w^

I managed to get all four keys and the hidden items, as well as enter the secret area, but I couldn't manage to ride the updrafts to get to the upper screen. :(