I recently became a Sudoku player. It's because of Good Sudoku, a newly released iOS app by Zach Gate and Jack Schlesinger. I wasn't looking to get into a puzzle game which is seemingly most popular among retirees, but it happened.
Good Sudoku is beautifully designed and a joy to play. The best feature is the Improve section, which includes a few educational subsections, "How to play," "Note taking," and "Techniques." So not only is the gameplay fun, but I can learn more tips and tricks to improve. The first dozen Expert puzzles took me around an hour to finish, but now I'm completing them in around 15min. I suppose the way Sudoku releases endorphines and dopamines is why it's so hugely popular. I get it now.
Two design complaints, though. One is that the "Hint" button is too close to the note options. It's too easy to accidentally tap that help button which immediately shows you a next move, a deflating feeling. And it instantly deducts a ton of points from your score (if you care about that). The other complaint is the UX around the note buttons. After hours of play, I'm still never confident when they're on or off, as they automatically disable after some actions but not after others. It often leads me to selecting a number when I didn't intend to. Sometimes I notice, and sometimes I don't. As a fix, I would drastically change the look of the number pad when any notation method is selected.
Small issues. No big deal. Five stars to Good Sudoku.
Update 8/15/2020: In the latest app update, both of these issues I had have been fixed. Gone. So, six stars out of five, now, I guess.