To me, the overwhelming failing of The Godfather, Part III, was the lack of resolution for the storylines involving Tom Hagen. Coppola has stated many times the original outlines for GF III centered around the Hagen-Michael Corleone relationship, but fell apart when Robert Duvall could not be re-signed to play the role.

Without getting into an argument over who was more at fault for Duvall's failure to return, was the resolution of the Hagen storyline important enough that Coppolla should have just re-cast the part?

I think Michael Moriarty, for one, could have played the part and brought it off credibly. There are probably many others who could have done it. Ed Harris for one, although he probably would have commanded more money than Duvall.