Mario Puzo's "The Godfather Returns" was a disaster.

Just kidding...about the author part. It was horrible, how stupid to change established facts! I stopped after a quarter of the way.

"The Godfather" novel was a very excellent read (even the parts about Johnny Fontaine once you got into it), but even Puzo couldn't follow it up successfully. The book "The Sicilian" had a small portion about Michael in Sicily during his exile, but even Puzo couldn't keep the timeline or facts right (I forget exactly what, but I recognized that Puzo was getting stuff wrong).