Most sudoku books have a lot of very easy and boring puzzles in them. This book is uniformly strong. It's not impossible at all. I never had much trouble solving any of the puzzles, but they are all pretty challenging. A typical puzzle in this book required me to take one guess, and be ready to erase everything after the guess, if necessary, and go back and follow the other route. This book is exactly what it claims to be, if you change the word "impossible" to "interesting". It's a lot better than most other sudoku books out there because they are just too damn easy.