I don't know if now is the time to think about that, but I felt poorly rewarded, I do understand that I should have felt great about passing each puzzle, but I felt like the struggle to solve them was not meaningful enough, all that was waiting for me was another of those puzzles.
(Don't take me wrong the puzzles are great and I know that this game is a puzzle game)
But maybe we could receive something more to direct our conquests, like powers that we can buy with the keys or something else. which can give me another objective than just going over puzzles.
I really liked the game, but I didn't feel like I could keep playing a lot more of those puzzles one after the other just because I want to challenge myself (maybe I should consider that its not really my type of game)