I'll add my counterpoint to this: even with Henley's cooperation, I actually thought the book didn't portray him in the best light. Some of the comments the author made seemed unnecessarily b*tchy in my personal opinion! Don's contributions are always referenced as "according to Henley" (i.e. implying "this is just Don's memory/viewpoint and take it with a grain of salt if you wish) however comments from others are presented as facts.
I agree that it talks very little about Glenn, and certainly doesn't do his talents justice. Indeed the overall impression I got was that the author was looking for "Dirty Laundry" rather than trying to tell the story of the band's creativity and music.