I don't think GF III was all that bad. Sonny and Fredo are two sides of the same coin. Sonny with his lack of patience and impulsivness and Fredo's niavety both give them serious handicaps in terms of living the life they were living. Sonny's death wasn't a surprise, the cunning enemy could use someone's weaknesses against them as they did Sonny and Fredo.

I think if Sonny had survived it would olbviosuly be a different story. He could may have became the Don, through succession, although in the past Vito has shown enormous wisdom and may have still went with Michael. I think what happened was Sonny's death just expedited the process of Michael becoming th Don.