I agree with all here. One of my astute co-workers noted, at the time the book came out, that "it reads like a first draft." Lively, interesting, terrific, but very rough around the edges. And, as Luca's Boy wisely noted, Puzo and FFC were smart enough to leave out all that Nino/Lucy/Jules/Hollywood b.s. in the film. That would have been the stuff I'd have advised Puzo to drop from the rewrite of the novel, if it had come off.
Puzo was one of those writers who couldn't resist passing along any and every factoid or bit of erudition he picked up along his road of life. I'm sure he put in all that crap about Lucy's gynecological condition because someone he knew had the same condition and had that operation. The Hollywood stuff is as a result of his having spent a lot of time with Hollywood types, and because his agent was connected to Hollywood. It's annoying in the GF novel, but it's almost unbearable in "The Last Don."