Some quick thoughts:
I think this would make an excellent entry-level Wharton novel for a young reader who does not fully grasp the realities of the Old World and the Old New York, but is ready to learn.
The protagonist, like many people in our time, strives after a certain lifestyle, the details of which become clearer with her apparently fairy-tale social ascent, as she grows aware of what is available, or unavailable, to her.
Even now, however, she was not always happy. She had everything she wanted, but she still felt, at times, that there were other things she might want if she knew about them.
Undine Spragg appears to me disturbingly modern; like another mesmerizing beauty, Marylin Monroe, she believes sensuality is overrated, and is only excited by men's power and what they have to offer; like Amy Dunne of [b:Gone Girl|21480930|Gone Girl|Gillian Flynn|https://d.gr-assets.com/books/1432019852s/21480930.jpg|13306276], of which Wharton's novel reminded me at times, Undine uses men as vehicles to attain her goals, discarding them once she notices they don't quite "fit into the picture".
Social criticism: 'The Custom of the Country' discusses not only social aspiration, mobility, and the increasingly popular institution of divorce, but also the tremendous cost of pretending the latter does not exist. More accessibly than in Wharton's other novels, yet still subtly, the author presents the realities of the changing social scene of New York, and the arrival of the parvenu 'invaders' entering the world and the lives of the Old New York high society:
What Ralph understood and appreciated was Mrs. Spragg's unaffected frankness in talking of her early life. Here was no retrospective pretense of an opulent past, such as the other Invaders were given to parading before the bland but undeceived subject race. The Spraggs had been "plain people" and had not yet learned to be ashamed of it. The fact drew them much closer to the Dagonet ideals than any sham elegance in the past tense.
Definitely recommended as an intelligent beach read:)