Do you include Part III in the saga?

The story ran its course in part 2.

Puzo never penned a part 3 of the novel and the fact that he resurrected Calo (who actually died in the books) and Un-aborted Vincent Mancini (Vincent's mother had her tubes fixed after aborting Sonny's bastard) the story for part 3 comes across as a cynical economic ploy by Paramount Studios to cash in.

As for the movie itself, it has a really solid performance from Andy Garcia who emotes an even amount of Corleone traits found in Sonny, Michael, and even Fredo. The story line however, doesn't make any sense from an economic and geopolitical standpoint. In no way would such a group like Immobiliare allow the Vatican's banker to entertain a take over by Michael if they were as corrupt and they turned out to be. Such an affair would have resulted in Michael being assassinated by real professionals too, not some senile goat like Don Altobello and his thug Zasa. In the end, the 3rd movie plays along like a maudlin TV series in the same vein as Puzo's other work "The Last Don" which itself was entertaining but wholly filled with half-ass Shakespearian tropes and Lifetime Channel oeuvre.

I basically see Godfather 1 and 2 as two halves of the same film. Part 3 is take it or leave it. Doesn't make me angry like it does other folks. I think the subject matter is pretty worthy. It's just not a very good movie.