I've been meaning to write a little something about Kim Stanley Robinson's The Years of Rice and Salt. Fitting to do it now that I've finished the book. It really is an amazing accomplishment. (Him writing it, not me reading it.)
A plot synopsis won't really get you anywhere. The initial premise is simple. It's an alternate timeline. The bubonic plague didn't just kill off the majority of Europe's population, but rather scrubbed the continent clean of human habitation. White people--or rather, those who would eventually self-identify as white--are basically extinct. (There's a small population in the Orkney Islands north of Scotland.) In the absence of Europe and Christianity, history consists of a long competition between China and the Muslim world.
That's right, a world-spanning Islamic empire. The novel was published a few months after 9/11, and there are some character monologues about Islam being a backward and inherently conquest-minded belief. But this should be taken as those characters talking. Both sides show progress, as does a third power that eventually rises in India. The idea of Orson Scott Card or Dan Simmons handling the same concept doesn't really bear thinking about.
Another aspect of the novel--one that really shouldn't be overlooked--is the fact that about half-a-dozen characters are reincarnated and come back to play their roles in different stages of history. We occasionally get to look in on them in the Bardo, a wait between lives as detailed in Buddhist writings. The characters come back in different forms, but the reader's knowledge that they are the same souls does make the very large-scale (about 1,000 years) more digestible. And there's a kind of interdependence, a way they all serve each other's journeys. Even the antagonistic character always given the initial "S" may be conscious of giving the others something to resist.
Might not be a perfect story, but Robinson has aimed at something unique and achieved it.