Wow, I really appreciate the in-depth feedback. It was reassuring to see you quickly work out what was going on in level 2 - that means my text prompts worked. I agree that the indicator should be clearer when you've got it right and you can move onto the winning space.
I can't blame you for getting stuck on level 4: one of the flaws of the concept is that it's hard to guide the player to the solution without showing it to them (like you said about the preceding levels). You either stumble into the right answer or you don't.
Anyway thanks for playing :)