5 stars: Absolutely fantastic puzzles, really challenging and enjoyable. No annoying ads. The best app if you enjoy variant sudoku. Sometimes, the smart hint system doesn't work properly, but the regular hints still do and they're really well written. Even if I'm stumped, I come out feeling as if I've learned something.
4 stars: Pretty good, but there are 2 issues on my android phone. First, this app uses a lot of battery. I think that is because the background is in constant motion while the game is played. Please let me turn that off. Second, it doesn't manage to save my results all the time. If I close the app and come back it will incorrectly think I still have to finish a puzzle that I finished before. Please fix these things!
4 stars: Great app for doing well crafted puzzles. Hint system is great but every once in a while the hint doesn't give you the info *why* something has to be true, just states it as fact, so I'm still stuck (eg 500k pack, puzzle 13, hint 4, c2). Would love to be able to flag that directly on the hint screen. Also had times where all hints were done and smart hints still didn't work. Killer calculator would be great on sandwiches too.
3 stars: The difficulty of these puzzles is kind of all over the place too. There was one that took me almost 9 hours, followed by one that took me like 10 minutes total, followed by one where literally the very first step required knowledge of some mathematical quirk of the combination of rules that had n...