I will start by saying that this has undeservedly be panned by just about everyone! The fact is it wasn't what anyone was expecting, especially from Guy Ritchie. What everyone was expecting was cockney geezers and good one liners "do ya like dags?" etc, but this is far more mature than his previous works. I would agree that it is confusing but all the facts are there for us we just have to see them and listen harder, this film demands all your attention! Look past the cool and dazzling look of the film, try to listen to the dialogue rather than admire the performances and i think we will all get a more thorough understanding of the whole film.
Yes this has its influences from modern classics( fight club, pulp fiction etc ) but it is in the whole original in both direction and pacing with a music score second to none. I feel that if everyone watched this film over and over they would understand it a lot more and maybe appreciate it for the fine piece of modern cinema that it is and i hope also that Ritchie continues in this vain as i far prefer this to his mockney "masterpieces".

Near the beginning of "The Godfather: Part III," Michael Corleone's son wants to drop out of law school and become a musician. Michael Corleone does not want this. But his estranged ex-wife, Kay, manages to convince him to let Anthony Corleone pursue music as he wishes. So he does.
That seems like an odd way to start a review, as it is a minor plot point and has nothing really to do with the major action. Just bear with me here; you'll see where I'm going with this eventually. Now let me tell you about the major plot. It is about Michael Corleone wanting to quit crime for good (he has largely abandoned all criminal elements in his family business). But then along comes Vincent Mancini, an illegitimate nephew, who is involved in a feud. So of course Michael must endure yet another brush with criminality and gun violence and all that good gangster stuff. Meanwhile, Vincent has a semi-incestuous affair with Michael's daughter Mary. Oh, and Michael and Kay are trying to patch up all the horrid things that happened at the end of Part II.
It is like a soap opera. One horrid, awful, 169-minute soap opera. Gone is any sort of the sophistication, romance, and emotional relevance that made the first two movies hit home so hard. After a 16-year break in the franchise, Francis Ford Coppola delivered a mess of sop and pretentiousness entirely incongruous with the first two films, once again proving his last great work was "Apocalypse Now" back in the 1970's.
What's worse, "The Godfather: Part III" isn't even a logical follow-up of "The Godfather: Part II." Michael is a completely different person. He hasn't just gone to seed (which might be legitimate, even if it'd be no fun to watch). He's become a goody-goody that's trying to fix all the tragedy that made Part II such a devastating masterpiece. His confession to the priest was bad enough, but that little diabetes attack in the middle pushed it over to nauseating. He also gets back together with Kay! For heaven's sakes, there is absolutely no way that should happen, as the 2nd movie made abundantly clear! She aborted his baby, and his Sicilian upbringing made him despise her for it. Didn't Francis Ford Coppola even think of these things?
And don't even get me started on Mary and Vincent's affair! For a romance so forbidden, it was shockingly unengaging. Sofia Coppola's acting did nothing to help. She made the smartest move of her life when she switched from in front of the camera to behind it, because she was possibly THE worst actress I have ever seen in a Best Picture nominee. Every line she delivered was painfully memorized, and every time the drama rested on her acting abilities, all she elicited was inappropriate giggles. In the climactic scene--I won't go into detail, but you'll know which scene I'm talking about when/if you watch it--she looks at Michael and says, "......Daddy?" I think I was meant to cry, but the line was delivered so poorly I burst out into long, loud laughter!
Now we get to the climax, and now you will also realize why I took time to start the review with a description of Anthony Corleone's musical ambitions. After 140 minutes of petty drama and irrelevant happenstances, Anthony Corleone returns... with an opera! So Michael, Kay, Mary, and Vincent go to see it, and for about 10-15 minutes a couple killers walk around trying to assassinate Michael. About this climactic sequence, I must say one thing: It was really good! But not because of the killers--they were pretty boring. I just really liked the opera. It had some great music and real great set pieces. And, from what little it showed us, it seemed that the story had echoes of the Corleone family's origin. I'll bet it was one swell opera, and I'll bet Michael Corleone was glad he let his son switch from law school to music.
My biggest wish is this: that Francis Ford Coppola had merely filmed Anthony Corleone's opera for 169 minutes and ditched the rest of the soggy melodrama. Better yet, I wish he hadn't made "The Godfather: Part III" at all. Part II gave us the perfect ending. This spin off was self-indulgent and unnecessary.
P.S. This is not a gut reaction to the film. I watched all 3 Godfather films over a month ago (though I was rewatching the first one). Not only does this mean that my expectations for Part III weren't screwed (in fact, I had set the bar rather low for it after what I heard), but it also means I've had a good time to think about all three films. While I was a bit disappointed with Part II at first, the more I thought about it, the better it seemed. But with Part III, it was bad to begin with, then got worse the more I thought about it. The sad thing is that many people will stop with Part I, but if they watch Part II as well, they will most likely go on to Part III. If you have the will, watch Parts I & II and pretend like Part III never existed.