Killer Sudoku by Sudoku.com 12+

Very good, except has started crashing after a minute of play.. update needed for new iOS? Unplayable at the moment.
When fixed should be able to turn off hints to avoid mistouch, and make the Notes On mode more distinctive, too easy to enter a number when a note was intended.

Addendum: The developers contacted me. Reinstalling the app has fixed the problem. Still not sure what caused the corruption, I think perhaps a low memory condition on the iPad in which case rebooting may have been enough, worth trying if it happens again. Commendable prompt service support, and they are now aware of the problem.

Hi! We are happy to know that the issue has been fixed. Please do not hesitate to contact us anytime if you have any questions.

I’ve done thousands of expert sudokus and this is an excellent way to make sudokus just that extra bit more challenging for those of us becoming bored of regular sudoku puzzles. A normal expert sudoku will take me an average of about 5 minutes. But the expert killer sudokus take me around 10-15 minutes. I would give this a 5/5 but the only gripe I have is that the hint feature isn’t nearly as useful as it is for the alternative regular sudokus. Instead it just gives you the correct number for whatever cell you have highlighted. Whereas, the original sudoku app gives you an explanation as to why a cell is what it is and provides a learning experience as well. I hope this feature is improved in the future because it would really help new users learn some of the unique aspects to these new type of puzzles. Thank you developers for making sudokus so accessible and fun for regular joes like us.

Hello Stephen! Thank you so much for your feedback. Right now, we don't have Smart Hints available for Killer Sudoku. We can certainly understand how that might be helpful But it doesn't fit our current development plans, but we'll keep your suggestion in mind. Thanks for bringing up your idea. 🤗

I love this game, play it every day. Have recommended this game to multiple friends. The ads can be annoying if you tend to pause the games a lot, but I don’t tend to do that so the ads don’t bother me much. I only tend to get ads in the middle of the game when I’m playing hard or expert levels.
The thing that’s really bothered me recently though is that I’ve been getting expert level difficulties for the past month straight for the daily challenges. Yes, I like a challenge, but it’s gotten ridiculous. I don’t know if it has a bug in it or something, but getting the same level difficulty every day isn’t fun, especially when it’s in the realm of being too hard for me. After a day at work especially, I just don’t have the brain power for that level of difficulty. I’ve just reinstalled the app, so I hope that’s fixed it, but just a heads up that this is happening.

Hi, thanks for your feedback. The Daily Challenges are generated randomly and the difficulty level may vary from one game to another. You can try to play usual games by choosing easier difficulty levels for several days, which may help with the level change for daily challenges. Please feel free to contact us if you have any questions.