I think the dev's goal has been towards balancing the difficulty not so much towards making difficult puzzles that are rewarding to beat, but towards making reasonably challenging puzzles that become rewarding to revisit and optimize as you get better at the game. In a way it sort of mirrors when you've just started learning programming, when every task takes large amounts of thinking "how am I even going to solve this?", implementing a solution that is sure to not be very optimal or even well written, vs. being an experience programming, when "how do I solve this?" is only the first step towards "how do I make my solution _better_?".
I hope we keep getting more Zachtronics games for a while; there really aren't too many games out there that are comparable to them.