In another thread Immobiliare brought up a variation of an old question:
do you think Tom had it in him to become a good Don?
Can there be something like a "good" Mafia Don?
To me, this question about a good Don is kind of absurd: After all we're talking about the head of an organisation that earns money by killing people. It's like asking "What makes a good dictator?"
Marlon Brando's strength was to show a complex character: A man who used his capabilities in a corrupt society who was still a good father and a loyal employer.
That doesn't change the fact that he was running a murder organisation. In "The Godfather" we see no street violence (apart from Sonny beating up Carlo), we don't see the killing of the labour union guy, we don't see how they blackmail shopkeepers. We don't really see how the Corleones make their money. We only see violence from the Corleone side when it comes to revenge which always shown as rightful.
Thus, a good Don is someone who organizes crime business smoothly.
