Loved it! Reminded me of games like Proteus, Abzu, that style of game that is super chill. I think you really nailed that vibe. Running around at high speeds is suuuper satisfying. Especially when you run off a mountain and you go flying, man it feels good. Those lines that appear while running were a nice addition. The music is super chill too and fits the theme perfectly.
That said, I do think that it's a bit lacking in other departments. There are no collisions, which is fine with things like trees since there are so many (though that depends on design), but having nothing is too little. Maybe you could have rocks with collision, because if there's nothing, it really just boils down to running wherever or directly towards the door nonstop.
On one side, I really like the map layout. As I said, running off mountains and flying around, going through the trees and besides lakes is really good. The problem is that passing through the door doesn't take you to a new level, just changes the color palette of the same one. So while it looks different, to the effects of what we think of it it's the same really.
I would also recommend to add something else for players to find! I explored for a while trying to see if there was something, until I fell through the floor and called it off. Having something that pushes players to explore is super nice in these kind of games.
I really think you got something going on here though! Running around feels good, jumping as well. If you had more levels, and other things to find, this could turn out as a really good full game!