An 18 month exploration alongside my blackbelt kakuro. I prefer killer sudoku because there is a greater variety of entry points that you have to find to crack each puzzle. The indicative times take for each puzzle are only that, because it really depends upon how long it takes you to find the key entry. Most of the puzzles flow quite easily once that first breach is made, but some towards the end of the book have multiple layers of defence. I could criticise the book in terms of the variety of difficulty of the puzzles and there were only a few that had me tearing out my hair. But given 18 months of pleasure for a small investment I think makes it worth 5*. If you are new to killer sudoku then start with something simpler. If you are a pro then few of these puzzles will really challenge you. The final 20 are roughly of the standard of those published in the Times on a Saturday.