True, his character I think is given more depth in the book, his true ideology is only touched upon in the movie, but never really explored.

Vito, basically didn't want to be subject to another man's will and was a man of his own making. The Mafia is romanticized in this mannor in the book, noble gangsters, people who don't bow to anybody else. Vito is a noble character but both him and Michael had the ability to be legitamite business men and it was stated in the book.

I think what Ebert is saying is Vito's choice (with Fanucci) and Michael's (McCluskey and Sollozzo) and ultimatly Michael's choice of allowing Vincent to take over in GF III, is their character's flaw. They had the intellect and ability to be leaders and very successful. Michael between GF II and III grew his fortune enormously and legitamized himself.

This choice would ultimatly rip apart their family and cause their children to suffer. This is a central theme of the movie. Fredo, Sonny, Sofia, all died due to their involvement within the life and although there is alot of glamour and romanticism in the life of organized crime it is ultimatly a dead end with more costs then benefits.