I would have made Michael less powerful, and made only Tattaglia and Barzini die, not Cuneo and Stracci (like in the book). Also, I probably would have made Roth whack Michael at the end of the 2nd movie, so they would be no Godfather 3 with its absurd ending. Really, no mafia boss can get away with murdering so many powerful adversaries and stay alive. Organized crime is based on balance, if a single individual tries to become an absolute dictator, he dies quickly.