I don't think Michael cracked up in II. The most wrenching emotional event in his life was Apollonia's murder. Before that he was still capable of love, of passion--even of playfulness, as we saw. But when Apollonia was killed, Michael was hit with the worst tragedy of his life. He was also saddled with the knowledge that the long arm of Mafia treachery extended right into Don Tomassino's supposedly secure compound--and that his wife was blown to bits by a bomb that was intended for him. After that, Michael was an emotional zombie. Sure, he had two bad shocks in II--Fredo's betrayal and Kay's estrangement and abortion. But by that time, he was too cold and self-centered to have been pushed over the edge. That happened in Sicily, years earlier.

Michael's life is a tragedy. The tragedy is in his choosing a life of crime when he had alternatives at every step in his descent. It's ther stuff of opera--which the Trilogy is in more ways than one.