Great system!
The zone changing system is the best part, it's like a puzzle piecer in a puzzle that is intertiwined !
I ussually don't like puzzle games, but this is awesome!
Ideas:
~ I think you should extend the puzzles, at the end there is around 10 zones, I think, if you added more levels, it should transfer to 20 or 25 or higher.
~ Implementing a puzlle creator would be awesome!
~ Add more door varients (Red door, green door, blue door) and more keys. Change up the level coulours a bit, if possible.
Would be 8.5/10, but since I enjoyed it so much, 10/10 ! :P