I am a Master's student of French with an undergraduate degree in French language and linguistics. I am also a French language proctor for proficiency exams.
This is the best advanced grammar book I have ever used. The explanations are in English to facilitate understanding with an English-speaking audience. The details in the book are completely nuanced and contextualized, giving you a very thorough understanding of each aspect of the language. Even reading the beginning section on "présent" or "passé composé" taught me a multitude of nuances that I was not yet familiar with.
Bref - buy the book. It's more than worth it if you're a serious student.
They should have a special shelf called, "books that I have loved and ingrained in my memory banks for all time." This one would be on that hallowed list. I read this over and over as an undergraduate, highlighted and underlined in a rainbow of reminders. Then, after a decade after graduation, I made a fatal mistake. I lent it to my dh's boss's wife and it was never seen again. But, I just saw an inexpensive copy on Amazon used and had to buy it in all its red-hardcover glory. I just wish it had all my notations about the finer details of the passe simple, subjective, and other crucial rules that my academic career depended on, "il etait une fois."