To be honest, I'm a little bit disappointed with the novel at the moment. I love the premise, but the book doesn't really seem to make the most of its setting(s). To provide continuity, the novel follows the souls of a small group of associates (a jati) as they reincarnate through multiple times and places through the centuries. But instead of fleshing out the broad trends and events of this alternate history, the novel focuses on the personal development of these souls across lifetimes. The result (so far) is a story which could just as easily been set in our own past. Hopefully, as the story goes on and as the histories diverge more, Robinson will give the reader a greater sense of how this other world differs from our own.
Wikipedia: The Years of Rice and Salt