Be very clear right from the start - this is not a sudoku book for the faint hearted! In fact, it is easily the most difficult - and therefore for me, the most satisfying I've tried.
I'd enjoyed (over a long period of time!) Gould's "Fiendish" books published under the Times banner but when I came to the end of that I was at a bit of a loss where to turn next. I tried the Tom Sheldon "Sudoku Genius" book which was difficult but annoyingly this documents and advocates a "trial and error" approach which to my mind is not true sudoku and the puzzles were greatly devalued as a result. I stopped after a dozen or so,
Due to the authors pedigree, the puzzles in here definitely have the right feel - no guessing required, but very very deep thought definitely is. Towards the end of his Times Fiendish Book I was getting great satisfaction in doing the puzzles without any pencil marks, i.e. purely by logic and brain power, but they would take me 30 odd minutes quite often
I have yet to be able to do a puzzle in this book in anything like that time, and certainly have not finished any without writing numbers in.
There is no messing about, it is straight in with the hardest level. The first one took me ages to complete until I got into the swing of it. I should also add that it is extremely worthwhile reading the advanced tutorials at the start, i finally understood the x-wing and swordfish methods which are essential for usage even after just the first few puzzles
If you like extremely difficult sudoku, are a fan of the Times puzzles and their associated logic, and most other books are either too easy or the puzzles aren't well formed, then trust me, you will LOVE this book.