GF III, of course, was trashed by critics who judged it strictly on the basis that it wasn't as good as I or II.

In my view, GF III was mortally hamstrung by the loss of Winona Ryder and Robert Duvall from the cast very late in preparation for the movie.

That made necessary throwing Sofia Coppola into the role of Mary. Now Winona Ryder is not exactly the greatest actress of all time either, but I think the role of Mary was trimmed down to accommodate Sofia Coppola's lack of experience. She did OK in my view but you do not expect actors in the GF series to do "just OK."

Much more damaging was the loss of Robert Duvall over a money dispute. This made it necessary to dramatically rewrite the script and write out the character of Tom Hagen and replace him with the nondescript B.J. Harrison aka George Hamilton who basically added nothing to the story except to say "yeah" once in a while.

From what i have seen and read, and ESPECIALLY from my reviewing of GF II, which was clearly setting it up, I am absolutely convinced that a conflict between Michael Corleone and Tom Hagen over the ultimate direction of the Corleone Family was intended to be the primary topic of GF III. IF Tom's loyalty was up for grabs, other families would certainly have tried to enlist him in a battle to take Michael out, which IMO would have been the main theme of GF III.

With Duvall out and Hagen written out, that whole concept went out the window, and the whole script had to be hastily rewritten and the entire Vatican/Immobliare deal inflated from probably just a minor topic originally, to the main story line of the movie. It all had to be done on the fly and that's why GF III seemed rushed and disjointed compared to I and II.