I thought Vincent’s transformation from a small-time toughie to a mafioso was pretty good.
Michael finds (at the end of his life) that he has no friends, he regrets killing his brother Fredo, and now his daughter is dead. He is given the chance to confess (by the Pope), but doesn’t take the offer.
It’s a truly Greek tragedy, where he knows he is doomed, but goes to his doom willingly. In a word, his soul is already dead, he’s just a walking corpse.