Chimamanda Ngozi Adichie: Americanah

At one point in Americanah, the protagonist criticizes someone for asking what a book was about because that question oversimplifies complicated narratives and people's interactions with those narratives.  In the protagonist's mind, books are about a lot of things.

That said, one theme throughout Americanah is the immigrant experience.  The protagonist is a Nigerian woman who spends much of her life living in America.  One friend, a European immigrant to America, mentioned that her immigrant experience resonated a lot with him -- everything down to the linguistic weirdnesses with American English seemed spot on.

Race features prominently as well.  The protagonist has a blog, "Raceteenth or Various Observations About American Blacks (Those Formerly Known as Negroes) by a Non-American Black," that breaks down a bunch of ways that race works in the US.  Those observations do a good job of driving home the idea that race is socially constructed.

There is poverty and success, depression and happiness, different types of relationships, and much more.  Americanah is a book about a lot of things.