The Good: The overarching positive of the book is its honesty. Joshua Harris even brings several personal battles into the book, which allows the reader to relate to its content. The honesty has a good balance of providing personal battles and not allowing the reader to drift off in their imagination causing more harm than good. That being said, it does not shy away from topics such as masturbation, pornography, and sexual fantasies.
Also, it provides great value in counseling. All throughout the book there are practical helps, homework assignments you could give counselees struggling with sexual purity, and Bible verses that combat false ideals and useful for withstanding temptation (chapter 9 happens to be my favorite chapter where it give Bible passages that dispel the lies of the enemy).
The Bad: The target audience (teens to young adults) took away from some of its firepower. You were forced to adapt some of the application as an adult reader.
The Grade: B+. The principles were still very solid and practical for the most part. It paints a realistic picture of the power of lust, and provides Biblical ways to combat and overcome lust. It provides a solid challenge to any reader, and great tool for anyone fighting for purity. Also, if you are looking for a book to counsel teenagers or young adults who are struggling in sexual purity, this book would be on my recommended list.