Worst scenes?

Part I - Damn. This is hard.

Part II - I personally didn't like the Hyman Roth assasination, the one at the airport. Too loose; the death of Roth's killer seemed too cartoonish.

Part III - The whole debacle of Vincent and Mary was definitely high on the ick factor. But I personally saw less conviction in Anthony's scenes of rejecting Michael. There was something so superfluous about his desire to become a performer; it almost seems as if he's only doing it just to ensure that he will not be part of the Corleone family of crime.