I've generated a series of sudoku puzzles using 9-letter words instead of numbers:
In theory it's a straightforward substitution, so the same solving methods apply. But it turns out that the brain works a bit differently with letters instead of numbers, so solving the game feels more challenging. There is less counting and more pattern matching.
But even the pattern matching ability is limited. By the time you finish a puzzle, you might feel like you got pretty quick at spotting the missing letters. But the next puzzle uses a different word. So it kind of resets the pattern matching intuition that you had formed. This keeps each game quite challenging.
Take a look, I published it as an online game here: https://wordsudoku.win/
I also have a printed book available on Amazon: https://www.amazon.com/dp/B09GZDT5JQ
I'm going to keep the book price at the minimum for a while (printing cost + Amazon fee), so feel free to grab a copy if interested. Feedback would be much appreciated.
For a few sample pages from the book, please see: https://wordsudoku.win/sample.pdf