A very late addition, but here none the less. These were my take-aways:
I believe this movie is a piece of art above all else, and everybody will take their own meanings from it.
I believe that it is intended to show that we make so many decisions in our lives without knowing the outcomes. As people we often reflect on the "What if's" of life, and it captures that quite well. However, the movie also states clearly that there are no wrong choices. It highlights that any choice that feels right in the beginning may lead to hardship in the end; it is just one of the possibilities of life.
In the end of the movie, it brings us back to the moment where he must choose which parent he must go with, I believe this is critical. Interestingly enough, after stating that this is the choice before him, it only comes back to one of his time-lines. The one where he waits on the bench and finds Anna; implying that with all of the choices before him that is the one he chose.
I think this is important, as it shows that when he made his choice the one he chose was the one that led to the most satisfying of love's. This implies that with the pursuit of fame, wealth, stability, control (Some of the achievements in the various lives) the pursuit of love was the strongest pull and something that he chased in each of his life-lines. This is also reflected in the scene where he lights the car on the fire to say that 'stuff is not as important as his relationship with his wife'.
There is a lot more to take from this movie, but I think that the points to reflect on are: The boy who sets off in life without knowing the path before him, the point of the old man looking back on the all the possibilities that could have been, and that we pursue love above all else. A few statements on human nature.