To continue from Turnbull's point somewhat, we must remember too: Vito was feared AND loved. People like Johnny Fontane did Vito favors out of genuine affection for the man--Out of a genuine sense of love and loyalty. Whereas people only feared Michael; They never loved him. Look at the way Johnny Fontane acts towards Michael's request that he perform at the Casinos: He's reluctant at first, but agrees because he'd "do anything for his Godfather." Michael was never a "Godfather"--Merely a Don. Michael couldn't care less if someone in then neighborhood needed a favor; These were meaningless to him. He was greatly feared, but was never as respected and loved as Vito was--either by his underlings, or by the other Families, or even by his own family.

He expanded an Empire founded on community, loyalty, respect and love, and made it an Empire which maintained power through force, or fear of force.

Michael probably would never have made it as far in the Underworld if not for the foundation Vito built. Michael, being EXTREMELY good in business, expanded on what was already made.

But if you put Michael in Vito's shoes, he couldn't start a Family and become the beloved and respected man his father was by 1945. He could make a feared Capo or Enforcer, but I truly don't believe Michael could've stepped out into the illegitimate world on his own and have built a family like his father did.

Also, I believe that Michael let his emotions and sense of hurt and anger guide his actions in killing Fredo and Roth. He had forgotten: What Roth did wasn't personal; It was business. Michael had made business personal. As said above, he admitted he killed Fredo because he "injured him". Michael thus "betrayed himself" by letting his emotions rule him. He wasn't an obvious hothead like Sonny, but had instead a cold, burning rage. But both had the same flaw: They took business personally, and went too far in their vengeance.

I've always thought that each son's personality represented a facet of Vito, and I think a flaw of ALL his sons--Michael included-shared was that none of them could truly control their emotions or separate their personal feelings from business. Vito, probably because of his upbringing, learned to separate the two very distinctly.

Ironically, the "son" who probably came closest to Vito, at least in terms of being in control of himself and not letting emotions guide his judgement, was Tom.