I watched it last night to wind down from my trip. Some observations:
(1) I had forgotten how good the acting was. Man Pacino was good.
(2) The Don was a much cooler guy than Michael. The Don actually thought he had some principles of honor, as opposed to Michael who was more ruthless. E.g. the Don refuses to kill the guys who attacked the undertaker's daughter, because that wouldn't be justice; he says, "We're not murderers." When Sonny is late to a meeting because he was cheating on his wife, the Don works in a completely unnecessary question about the visitor's family, solely to be able to indirectly tell Sonny, "A real man keeps spends time with his family" (or something like that). After Sonny is killed, the Don says he wants no inquiries and no retaliation, and calls the families together for a truce. He initially doesn't want to deal drugs, but capitulates when he sees how much the other families want it. Finally, he swears on his grandchildren that he won't break the truce (assuming nothing happens to Michael on his way back home), and he fulfills that pledge. In contrast, Michael doesn't forgive anything and lies all the time. And of course, the Don's last scene where he is playing with his grandson is adorable. Granted, if people want to give me all sorts of counterexamples, go ahead, but my point is that I think Puzo / Coppola were trying to show that the Don really wasn't as bad as he first seems.
(3) I had never noticed this before: In the scene where Sonny beats the cr*p out of his brother-in-law, there are three other mobsters holding the crowd back. I.e. the neighborhood would have intervened if some lone guy started wrecking a guy like that, and it took three other (obvious) mobsters to keep the public from interfering. Very interesting.