I'd read Tarkington's other noted book, Alice Adams, some time ago, and only remember so much of it. Ambersons seems more memorable as it progresses slowly as a morality tale set during the turn of the century. Young George Amberson Minafer grows up as a spoiled brat into an equally intolerable adult. He is in love with a young woman from a family of means, but too proud of his own lineage to care about hers. George's family represents the old wealth and refinement of the past, while Lucy's family looks toward the future - industry and forward-thinking. Revelations of romantic entanglements (George's mother was one fond of Lucy's father, and that affection never really died) spur George into acting more selfishly to the point it nearly ruins him. If there's a lesson to be learn here, it's that people rarely do remember who comes in second place.
You have to read these older books with great patience. Tarkington's style was a bit sluggish to get through over the first parts of the book, but did pick up toward the end. Worth a read.