The title of this book is misleading, since to me, "Mastering Arabic" implies gaining complete fluency, while this book is targeted at students who have little or no Arabic ability. So if you have already had an Arabic class or two and have some ability in the language, look elsewhere. This isn't a book for raising the fluency of existing Arabic students to the next level.
For its intended purpose, however, "Mastering Arabic" is pretty good. It starts out by teaching you the Arabic script (necessary for any serious student -- stay away from books that transliterate everything into English letters). Then in each chapter, there are some short grammar lessons, a number of activities, and some new vocabulary. The activities range from fill-in-the-blanks exercises to reading newspaper headlines to matching pictures with sentences to crossword puzzles, and so on. All are at a pretty basic level, but they do provide you with "authentic" Arabic usage.
"Mastering Arabic" is really intended to be used in a classroom, or with some tutoring by a native speaker. If you are learning Arabic for self-study, the lessons do proceed gradually enough for you to be able to use this book on your own. However, in that case, I would recommend buying the accompanying audiocasette tapes (you can order them through Hippocrene's website).
This book is at an "Intro to Arabic" level, but it is far above the level of your average phrasebook or "Arabic for Business Travelers" or similar books intended merely to teach you some basic conversational phrases. When you finish this book, you should be able to handle "survival Arabic," which is to say, you'll be able to manage simple sentences and communicate everyday ideas, and your vocabulary will be adequate for basic communication. If you want to go beyond that, such as being able to read newspapers or watch Arabic TV or carry on more complex conversations, you'll need to find more advanced books and learning resources.