I really like the execution on this. One piece of feedback is that the timer gave me anxiety and I closed it. I do puzzles to phase out from stress not to challenge myself in a time bound environment
I hear you. I personally found the game less interesting before I added the "threat" of losing stars — it felt to me more like trial-and-error work. However, I think there is value in embracing its more meditative side and offering untimed (and I supposed, star-less) play as well.
If you just show the number of stars the player got at the end without emphasizing what they missed, those who are playing for speed are rewarded with more stars, those who are playing for low guesses are rewarded for a low number.