Neat idea and execution. Hope that there will be more.
I think that "ground" tiles should be more clearly separate from "background" tiles. At least once I thought that I can make a jump and was blocked by something I thought that would belong into background. Also I think that some challenges are too precise. A little bit of leeway would make it flow smoother.
In all other ways I think that level design is just right. I always had some kind of clue where to move next, even without any instructions. Challenges were fun and it is nice that new mechanics emerge through different creatures that have their own purpose (love how snails work as shortcuts for cleared challenges). Music is awesome.
I had some performance issues on browser, which I guess is to be expected.