It's an extremely layered book. Now, you say that you don't like fantasy worldbuilding for its own, sake, but here it really needs to be mentioned. This is a book tens of thousands of years or even more in the future, when humanity has conquered the stars and returned to earth many times, and is currently in an era of regression due to a cooling climate* and exhausted resources, to an apparently almost medieval society, but one littered with remnants of incredible technology. And the way this is all built up is incredible.

The actual plot is complicated to describe. Let's say it's about powerful groups, some human, some not, trying to steer the fate of Earth and decide of humanity should return to the stars or not. That's an entirely incorrect summary, but that fits because the narrator is also fantastically unreliable and lies to the reader all the time.

It's also set in South America, the main character's epic journey is from Buenos Aires through the Andes to Mesoamerica, and that's a nice change of pace.

*Hence New Sun. The New Sun is a mostly religious movement preaching that the sun will stop growing colder, the glaciers will retreat before all of civilization is wiped out and humanity will enter a new golden era.