I have also read it and it's a good read, albeit very long, took me like a year cause I kept putting it down then picking it back up. There are some great details as mentioned by mustachepete, and there are a lot of scenes that I believe he wanted to shoot that he just didn't have time for or just didn't make the cut. The only "pitfall" with this book is Coppola's handwriting—I could barely read it, and missed out on a lot of his notes. There are some funny things he writes to himself, I can't remember exactly but some of it is like "Don't fuck this up Francis!"

I do hope there is something in the works like this for GF2 though!