Quite a fun game! Played all of it :p
I don't think difficulty setting are that necessary, I do think I'd prefer to have checkpoints in each area so we don't have to start from the beginning every time. Right now it's not that big of an issue since the game is so short but it might become more of a problem if you make it longer. I like the puzzles, they are quite fun, I just wish there was more levels!