I'm beginning to wonder if I'll ever take the time to view part III. Is it really so bad that I should avoid spending a few hours of my life to watch it?
No, watch it. However, given the possible story that could have been told, and given the quality of the actors available (Pacino, Keaton, Shire, reprising the roles they had filled superbly earlier on - and the newcomer, Andy Garcia, the only decent addition to the cast), it could have been very good. But it lacks depth, both as a story, and as a conclusion to an epic tale, and, given the quality of what preceded it, it is (unfortunately) a huge letdown.
The story that might have been told, wasn't; we never get to see Michael's emotional and intellectual journey - and that was part of what we saw in the earlier movies. We never get to see how he came to the dark night of the soul - as in realising that this was where he has arrived at, and how to deal with that; we never see how he lived in the twenty years between this and the earlier movie.
Also, there isn't a deeper story to tell; the enemies without don't really matter, emotionally, or narratively, in the third movie.
The supporting cast of rich characters who made the two earlier films such a convincing and character filled, multi-layered, nuanced tale of someone (Michael) finding their way to the dark side and, as a consequence, 'gaining the world but losing their soul', losing themselves and everything they loved en route, are missing. Thus, as a consequence, the challenges or enemies besetting the family don't really register in the third movie. We need the 'family' - and their supporting cast - present, to give this story depth, and, as they have either died naturally (Mama Corleone - her death was a great scene in Godfather II), or were killed, (countless members), or murdered, or were driven away, there is a curious lack of 'story' to tell in the third movie.
Then, there are the famous casting issues, too; Michael's children are simply not believable, neither of them, and, because of that, their stories don't work. Nor, because of the narrative shortcomings and casting shortcomings is Michael's relationship with them (or Kay's, for that matter) credible. You don't believe that Michael passionately cares about them, the relationship is never given time to develop, and you don't see that it matters, because they are so poorly portrayed (and miscast) - and indeed written - so, the ultimate tragedy, as in the price he must pay for what he has done (in the past), doesn't have the impact it should have because they are so poorly conceived and told.
So, the Godfather III lacks both elements of what made the earlier movies epic; it lacks the necessary external narrative arc to drive the story and effect actual character change, as well as give narrative tension to the tale to be told; and it lacks the endlessly fascinating dynamic of the internal incredibly complex and myriad relationships within the family as they, too, respond to what is happening both outside and inside the family, and, also, respond to each other as a consequence.
