These offer a real challenge. If I'd known just how complicated some of the puzzles could be I might have thought twice, but then I'd have missed the fun of completing them. All the books (levels 1 - 3) were delivered together, quickly and well protected against damage. Each level is well worth buying if the usual compilations are losing their edge and proving to be less enjoyable. Be prepared to re-awaken the addiction that brought you thus far! There's also a companion volume to help you master the techniques you need to solve the puzzles. The ideal package for the dedicated Sudoku addict, especially with Christmas on the way.