The concept is solid and the art style works. I really like the sound, as simple as it is.
However, it's been said a couple times, but it really needs to be said again: the auto jumping on land when space is held needs to go. A lot of games have jumps that get higher when you hold it, so it's a common habit for people to hold down space when jumping. In this game it becomes a worse problem than it would be in others due to the switching mechanic. One accidental jump means you have to do an entire sequence of jumps again. Also, this game suffers from the issue that many platformers do, where it feels there's not enough leeway around edges, so you'll wind up feeling that you've pressed jump in time but instead rushing off to your death. A little extra collision on the platforms should solve that easily.