I hadn't really been interested in this book, feeling that the setup was a bit naff. It's an alternate history told via short sections about the same few people reincarnated at vaarious points in the history. Which sounds pretty dumb, really.
However, it's actually good. The structure is just that - a way for Robinson to muse a little on the nature of history, religion, science and humanity. He has some thought-provoking musings in there, too.
Also, I'll save other readers some confusion by mentioning that each character has the same initial every incarnation. So pay attention to the names (I didn't pick up on this until the third section, so I think I missed some characters in the first couple).
The Years of Rice and Salt (Amazon)