This is a wonderful drama, social, human and familial. As all good classics there's more to the story than just surface plot. You can see it from multiple perspectives, among them the social one is always very present in Vidor's films.
But first of all this is a great, great movie. One of those that will make you cry in a couple of scenes at least; if you don't, you'd better check your pulse.
Now, here are the subterraneous plots that I see:
1) The familial, the relation between a divorced father and his little son, whom he loves immensely and by whom he is likewise corresponded. This, actually, is not a plot but a naturalistic depiction of this relationship thru story details and characterization.
2) The social. The incompatibility between high-class minded people and simple minded/humble people.
3) The individual relationships between the three main characters or roles: the uneducated and loving father, the apparently educated and classy mother and the innocent child. This triangle gives a lot of food for thought about the mysteries of the human soul. And every viewer will have his own take on this side of the story.
I hope we'll be able to see soon on dvd more of Vidor's great classics, like "The Crowd", "The Fountainhead", "Our Daily Bread", or the great "The Big Parade".
One more thing: The quality of the dvd is exeptional. It doesn't seem like you are watching an old movie at all.