One review of this book describes the main character, Chase Insteadman, and his astronaut fiancee, Janice Trumbull, as both being "adrift." That's the best way to put it, I think. Jonathan Lethem, the author, grew up in pre-gentrification Boerum Hill, Brooklyn, and has written at least two novels I know of about those hard-luck streets. Here he's taking on a very different type of subject matter: Manhattanites who have sold out, come unglued, or, as someone else described it, gone adrift.
Chronic City isn't a self-involved meditation on privilege and the lack of meaning in modern life, though it can seem so at first. It's about how modern life in Manhattan, and maybe the rest of the U.S., is driven by nothing more than a desire to be entertained. In Insteadman's Manhattan, The New York Times publishes a "war free" edition filled with updates on a tiger that's said to have escaped from the Central Park Zoo, and dispatches from space, where a tragic group of astronauts are floating forever with no way to get home.
Neither I nor Lethem is the first person to reflect on how New York City, center of so much that happens in the world, can often seem like nothing more than an amusement park for the insanely wealthy, shockingly idle, and impossibly privileged. To say anything more would be to give away events that happen more than 200 pages in.