1st has to be Michael's flashback to 1941 at the end of GFII. Apart from resurrecting so much and reconstructing the characters to be almost unblemished, not to mention creating a wholesome scene, it also grants the user a sight into Michael's soul at the moment Fredo is killed. We believe he has done so coldly and callously, and here we are seeing a man fully aware of what he has just done and the moral burden that goes with it. However, the sheer power and significance of this scene is such that it takes the viewer back to the logical beginning. This is the very moment from which Michael's life diverged and started the long path to where he was now - utterly alone.

2nd has to be the opening dialogue in GFI between Bonasera and Vito. We simply see Brando the colossus giving us a brief but telling glimpse into most if not all facets of the Don's character. Bonasera is genuinely offensive at times but what we see is someone who is able to measure his aggression and dispense his power carefully. He also displays protocol and the utmost courtesy. We are being led into the culture, in other words.

3rd is the alienation of Kay from Michael. In fact, the scene is utterly dominated by Kay's revelation of her abortion and, of course, the visible changes in emotion in Michael's face. It quite takes the breath away and just shows how not saying anything often demands more from the actor. Of course, the final explosive outburst is the final time we see any revealing from Michael until the flashback scene at the very end of the film.