I'm with the flashbacks are what elevates the whole movie, character crowd. We get a much deeper perspective on things.
I was with one person who insisted the pattern of the rug that young Vite and Clemenza steal - is the same pattern as the carpet outside the hotel room in Washington where Anthony is playing while Michael and Kay are arguing inside --- thoughts anyone?

The point of the flashblacks reminds me of one of the early cuts of The Deerhunter, where the whole sequence of the wedding at the beginning was cut - but audiences didn't find the characters, as a resultthe whole movie as compelling as those who say the full length version.