It shouldn’t have been a trilogy. That story was finished at the end of Part II.
My dream is that they’ll make Part III.2 and just pretend that the original III never happened.
The story was finished in Godfather II, but the Man, Michael Coreleone, was completed in the third film.
It was about his search for redemption, the man who looked back on his youth and his initial resistence to the family business, and the regret and frustration at his choices which pulled him into evil.
I thought the film, and its final scene, was brilliant.