I admit when I'm wrong.
And boy, was I wrong!
The first third of The Godfather novel is nearly a shooting script for the novel, but after Michael escapes to Italy after killing Sollozzo and the police captain, the novel becomes a rushed mess that doesn't know what it wants to be.
At first, I enjoyed the expanded Johnny Fontane story arc. It quickly becomes a criticism of Frank Sinatra's Hollywood lifestyle, and his childhood buddy Nino Valenti is a poor stand-in for Dean Martin. Connie Corleone nee Rizzo has been moved out to Vegas with her abusive husband and shacks up with a hot shot surgeon who became an abortion specialist because "surgery was too depressing," because people wouldn't listen to his infallible wisdom. This section reads like a crap pulp scare novel and I couldn't help but imagine the Doc wearing glasses and talking around an unlit pipe that was always in his mouth. It's beyond parody. This is where Connie's vaginal "problem" becomes an entire story arc, after the Doc wags his finger over her "primitive beliefs" and explains in excruciating detail how pelvic floor surgery can give her a world class sex organ.
This reads like bad mid-century soft erotica. Notice I said bad; I've read plenty of good, entertaining novels of that stripe by Lawrence Block under pseudonyms. Mario would have done well to read them, and not be so clinical. The only reason for Connie's sexual awakening, which culminates in the line, "like a carpenter hammering together pieces of two-by-four, the doctor was building her a new snatch from the ground up", is so she can introduce the good doctor to Johnny Fontaine, where he immediately diagnoses his weak voice as cancerous polyps on his larynx. He shaves off the polyps and saves Johnny's voice, but can't save Nino Valenti from drinking himself to death. I wonder if Puzo was disappointed that Dean Martin lived to be nearly 80 years old.
The novel descends into exposition rather than action, with Michael taking on the mantle of Don with natural ability, becoming a more ruthless version of his father. There is little tension for the back half of the novel, and the only interest for me was nostalgia, as he praises the "primitive" ways of country Italians and how much better it is to marry a virgin like they did in the old country, than have to send your wife in for vaginal reconstructive surgery, like they do in liberated '60s America! All Michael does for two years in Italy is walk around with two bodyguards until he sees Apollonia, the virginal yet sensuous nymph of few words (I think she says five?) that he pursues to marry. They have sex and then she gets blown up in the car, in a scene that is just as stupid as the one in the film. She's never fleshed out into anything but a simple sex object and is killed so he can pursue Kate, who he must bend to his will now that he's a Don and not a "college boy."
My pet theory is that Puzo sold the novel before it was completed, and had polished up the first third. Once the advance and PR hype took hold, he rushed the rest, which has the expository feel of a first draft. Coppola was smart to cut the Fontane and Connie subplots, but he somehow managed to make a 175 minute movie out of what's left. In the book, the fight over Vegas with Moe Greene (a Bugsy Siegel stand-in, he's killed the exact same way as the real mobster) is rushed and not explained; we only see the aftermath. In the movie, they change his murder to the infamous eye shot because Siegel was shot five times with an M1 carbine, twice in the head, which popped one eye out of its socket. The book is so rushed by this point that the Corleone's rival is dispatched in a single line, in a master stroke by Michael, whereas in the beginning, they obsess over every detail of how to get the gun in the toilet for the hit on Sollozzo.
Is the book worth reading? It was certainly entertaining, even the bad parts. And it serves as a good lesson of what not to so with the second half of your novel.