Godfather III can be summed up in, fittingly, three words:
No Duvall. Sofia.

Of course it's only the beginning of the film's shortcomings, but these two are the worst ones. Duvall's lack hurts the film badly enough, and FC's nepotism in casting his wooden daughter proved to be the very worst flaw of the film and probably the worst casting in the entire history of motion pictures.

When I watched the Godfather III DVD, after a while I had to take a rubber chicken from a drawer and put him in front of the screen whenever Coppola showed up, to conceal her. I could still hear her painful delivery in that annoying voice, but at least I did not have to look at her anymore... And, quite frankly, with a rubber chicken instead of Coppola, the movie became almost watchable. It also helped a little that, when she whined "Daad..." in that infamous climax, I muttered "You sure are. Too bad it happened so late".

Perhaps I'll even try it again, this time with a photo of Duval during the Hamilton scenes...

Or perhaps FC himself should ask George Lucas to do a CGI "Godfather III Redux", with Coppola replaced by an actress and Duval inserted over Hamilton... and, even better, with everything except maybe for the last 20 minutes reshot.

I suspect those who actually try to defend this film only feel compelled to do so because FC, Pacino and Puzo were involved in its making. If it was an identical film directed and written by someone else (but still without Duval and with Sofia Coppola), I have no doubt that literally almost everyone would have been listing it as one of the "worst sequels of all time", next to such antifavorites as "Highlander II" or "Batman and Robin"...