I am seriously addicted. I have about half a dozen sudoku books scattered around the house. Whenever I have an idle moment or am waiting for someone, I pick up a book and start filling in those crazy numbers. I prefer the medium-hard to difficult puzzles. There are certainly some that are extreme that are too hard for me. But I do like being challenged. With the medium-hard ones, I try to do them without any little "numbers in the corners" It's so satisfying to complete a puzzle with no marks, notes or erasures! I am also noticing that particular authors (or whomever is designing the puzzles in a given book) have their own style and the puzzles have a unique feel to them.