Ending?

Everybody was pissed at Michael except Fredo. Fredo supported Mike's enlistment. I don't know if that was the point of that scene in the movie, but we can imagine that Mike is remembering his past days with Fredo, and that Fredo was the one who gave his blessing to Mike's decision. Not his dad, not Sonny nor Tom. Only Fredo, the brother he had killed.

They are showing us everything Michael has lost: the brother who was murdered, the brother he murdered, the adopted brother he has pushed away, the idealism he once had.....

Forget it Jake. It's Chinatown.

To speak to how you did for Robert DeNiro, he was the first actor to do almost all of his dialogue in Italian, and had too take on a role of one of the best actors whose performance won an Oscar. If you think about that time, people saw how DeNiro took a role, that was still Brando's character, and make it his own. He won an Oscar through playing the same character in a different light, and doing his dialogue in a different language.

"The best laid schemes of mice and men Go often askew, And leave us nothing but grief and pain..."
From the poem: To a Mouse, on Turning Her Up in Her Nest with the Plough"
-Robert Burns 1785

From the beginning, it was Vito's plan that Michael would be the family's foray into the legitimate world. Likewise, it was Michael’s plan too. However, upon Vito’s attempted assassination, Michael felt compelled to help his father. Michael’s actions led to his plans going awry.

By the end of The Godfather: Part II, we see a flashback of Michael as he was and then a picture of what he had become. Michael has the blood of so many men on his hands – including his brother. To underscore his pain, Michael is also estranged from his wife. Sitting alone, victorious and broken, with his plans in ruins, he might be thinking back to the day of his sister's wedding when he said:

“That my family Kay. It’s not me.”

You all have made so many good comments on this thread. They were great to read, and very helpful.

In the first film after Sonny dies and Michael becomes Don, Vito talks to Michael and says he didn't want that life for Michael. He goes on to say that Michael would be a normal man, but a powerful man being a Senator or a Governor. Michael went in the military to get away from that life style, but slowly but surely, he does get mixed into the crime business. It shows a flash back of that scene of his family then fast forward to the end of the second part of the film. He's old and alone. Parents have passed away, Sonny was killed, Carlo, and Freddy as well. Tom is gone, Connie and him don't have the best relationship, and Kay and him have separated. It goes to show how much things change by the decisions we make in life. Basically, it's was portraying how much things have changed.

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The point was to show the final contrast between the past and the present. That was a major narrative theme throughout the film, with Vito's rise and gaining a family contrasting with Michael losing his family and his personal downfall.

In the final flashback the contrast is also ironic and tragic. We see that Fredo is the only one that congratulates him for enlisting. When the scene concludes, we also see that Michael's decision to defy his father's wishes and enlist has left him alone and isolated at the dinner table. Yet the path he's chosen is one of more promise.
Cut to the present and that promise is gone. We see Michael alone again in his compound - his personal choices and decision to follow in his father's footsteps leaving him isolated.

The image preceding this of his father holding him as their train departs the old country symbolises that his family and traditions gone. That Michael's desire to maintain and control his Family in the more modern age has left him broken and alone.