This is a really good game concept. I love it. The music and art are good too.
Here are some 'issues' that I caught while playing the game:
- I think the world change door animation should be a bit faster.
- It would be good if we can look down to see what's below when no platform can be seen from where the player is standing.
- I assumed that I should be dead after falling down the hole, but I was stuck and can walk 'below' the level.
- I don't know if this was intentional, but normally the player will move with platform when it moves horizontally/diagonally too.
But overall, good job!