The book is not great. It goes on and on with stupid subplots (for some reason johnny fontane is an important character, go figure). Coppola hated the book and hesitated a long time before accepting to work on the movie.

The 3rd party is not on par with the other 2, but it gets more hate than it deserves. It is the closing of the Corleone saga and I found the 3rd act of the movie very powerful.

When I first started dating my wife she had never seen it and we watched them together. "Whoa, they really don't make them like that anymore" were the words out of her mouth.

While part 3 is a huge letdown, if you treat it like an epilogue (which I think Mario Puzo has referred it as) then it's easier to watch.

the third, while the weakest, is still worth watching at some point just to see how Michael's crazy story ends. sofia's miss or miss performance really drags it down though.