Matt Kraus’s review published on Letterboxd:
I have seen the first two movies about five times each (obviously), but I just never had any interest in sitting down with this one. Its reputation is middling, certainly, but beyond that it just always seemed like the definition of a movie that had no reason to exist. Parts I and II tell you everything you need to know, and any pitch for a potential Part III seemed like it would be "and then some more stuff happens."
And, indeed, that's basically what it is. Did I still mostly like it? Yes, but any time you combine this style of filmmaking with the usual "Godfather" music cues, that's an automatic three stars right there. This is a gorgeous universe to live in, and I would give up a limb to see a movie that looks half as good as this in 2020.
The problem is just how disjointed the actual content of the film is, and a series of performances that just feel disconnected. Obviously Sofia Coppola's work has the worst reputation, but that is way overblown—I was surprised to see how little she's actually in the thing. (Though to be clear, she is basically a blank slate, and I think that's partially the fault of the writing. I'm not sure what a good take on this character is from an acting perspective.)
The biggest problem is actually Al Pacino, who is not bad in a vacuum, but this Michael Corleone just doesn't seem at all like the same Michael from the first two movies. In the time after Part II, Pacino obviously drifted away from the more bottled energy that made those first performances so stunning, and here you have work that is fundamentally too "big," but you can also feel him trying not to go that big, so you wind up somewhere in the middle, and it basically falls flat.
The movie around him also just feels too big at times. The sequences of violence are at a larger scale and frankly a bit absurd, and the plot slowly lurches forward without any real overriding purpose. When Joe Mantegna's name shows up during the end credits, I had actually forgotten that he was in this same movie. It felt like ages ago.
I will say I quite like the end of the movie, which seems like a controversial opinion based on the reading I did after watching. It would work better if the studio allowed Coppola's preferred title of "The Death of Michael Corleone," since then the bleak "joke" of it all would land a bit better.
Anyway, it turns out I had a lot of thoughts about 1990's "The Godfather Part III," huh? I mostly liked it.