Michael looks contemplative of the future, as in, "What do I do next?" He's eliminated his enemies and stands at the top, alone. But, "alone" also means he's lost his parents, had his brother killed, and lost Kay. He has his children, but I think he saw them as possessions, not as the jewels of his life. I also don't infer any regret in Michael's looks--perhaps melancholy.

Like Woltz, I don't think that the flashback scene that follows is a coincidence. Perhaps Michael is contemplating the idealistic youth who signed up for the Marines on Pearl Harbor day with his current self. Again, I don't infer any regret from the cold hearted bastard.