This is probably the best Gotti book available which isn't saying much when the main rival is by the same authors. It's a fairly decent book with plenty of information on Gotti and his crew but a lot of it is questionable.
The main problem with the book is that it's outdated. First printed in 1988 before the Gotti saga had ended or at least semi ended when the once named Telfon Don for his ability to avoid conviction finally was put away. This "updated" version is only updated with a few extra chapters at the end and they very much feel like they've been rushed and just slapped. Probably because John Gotti had recently died at the time and the authors wanted to cash in on it.
This book could have been a lot better if instead of sticking a few extra chapters at the end, the whole book was reworked. Because upto chapter 28 it is still based on information from 1988. You read it and you think they could have atleast updated it with all the information provided now.
But that's Gene Mustain and Jerry Capeci, I wouldn't expect anything more from them.