This might be the most complex piece of writing I've read. And not just for its florid writing.
On the surface, a social commentary about the mores and dictates of late 19th century New York, it felt like much more than that to me. It's not as if any of the crazy shenanigans surrounding society - and by society, I mean any kind in any place - have disappeared. There are still rules, although they may have become more relaxed. There is still old money and new money and how people are treated if you come from one versus the other. And there are still problems in marrying or courting above or below your station - again, no matter where you come from.
The novel tends to age well, since it tells the story of society in general, not just that of New York in its time. It's as if nothing has changed, and our culture is not more enlightened 100 years further on. For instance, never does Mr. Rosedale appear that his manner and forbearing are not associated with the fact that he is a Jew. For all Wharton's obvious liberal attitudes, she was not able to bridge that cultural divide. Upbringing? Lack of education? We struggle with those to this day.
Far more interesting, though, is Lily herself. You want to whomp Lily over the head, bringing her to some reasonable sense of where her life is going because she cannot be reconciled with her own desires. She wants to be morally upright, but she also abhors anything not beautiful and expensive. That conflict makes it impossible for her to choose the right path, time and again. I understand how that could work in her head, but the ending makes you truly wonder if anyone would choose this path, lacking any foresight about where it can end. That makes her a true innocent, more than anything else, and I think it's likely that Wharton could never have told this moral tale without an innocent at the center.