A pretty decent textbook
As a Westerner trying to learn a language with a totally different alphabet, I am finding this book to be very helpful. Words and phrases are given in both in Persian and in English transliteration, which helps you pronounce things properly. The explanations of grammar can be somewhat technical, but not usually TOO technical to be understood by the average person. The exercises are very good and comprehensive. Although my instructor, a native Persian speaker, feels the chapters are "mixed up" and should be ordered differently, I'm not having a problem with that.
The main disadvantages of this book are, first, that the dictionary in the back is NOT at all comprehensive with respect to the words actually used in the book, and not all words appearing in one half of the dictionary will appear in the other half, making it difficult or impossible to find some words. A separate dictionary is advisable. Also, the typeset is WAY too small. A magnifying glass is a must in order to see the number of dots, loops and tinier symbols used on many letters.
Overall, this is probably the best book for learning Persian on the market at this time.