Well said, Cristina, I've been trying to find a good reason myself for ages and you know what? I concluded that this character is by no means just a villain. Not the typical, ordinary one, anyway. Of course we all know he is a criminal, a murderer. No question about that. But when we deepen inside him, when we consider where he comes from, his personal story, we also perceive another aspect (maybe the most remarkable one) bringing us to be merciful towards him. He was in fact both a victim and a torturer. And the first one who was to be a victim was indeed himself, his whole life being devastated by the impossibility to escape his own merciless violent fate. We realize it and cannot help but take pity. That's why we sympathize.

Add to this moral reason (that is undoubtedly a good one), the subconscious appeal of evil to humans. And Michael's character is decidedly fascinating due to his ability to live against the common rules, at the edge of society, in an absolute outward coldness.

Last but not least, consider the P-factor. By P-factor I mean the Pacino role. He was in fact the perfect Michael, the perfect victim and torturer, an archetype we can detect in his most significant roles throughout his brilliant career. And you know why? Al Pacino got those eyes. He got some inner flame in them. Pacino's eyes say it all. You look at his eyes and you see lust for power and thirst for violence, coldness, rage. But somehow, at the same time, you see desperation. And a vulnerability, desperately calling for help. A calling that in Michael's case is to be left unanswered, at least during his life. But I believe God will answer. I like to think of Micheal finally calm and pacified, soon after his solitary death in that Sicilian sunset, among crickets songs and oranges aroma. The Don is dead. Michael lives.