Rating: WARTY!
This is a seven-hundred sixty-some page tome of a tombstone of a novel, and the reason for that is not that there's a huge story to tell, but that the author is so obsessed with world-building that he forgets to actually tell a story.
It's supposed to be about two sisters: clone-twins in a world where winter twins are nowhere near as appreciated as summer twins - why is never really explained. Rather than stay with their clan as summer clones do, they must leave to seek their fortune. It takes almost a hundred pages - a seventh of the story - before they actually leave the city! Most of those pages are taken up with world building - in a world they're due to leave, so why expend all that time on it?
If it had been done beautifully, that would be one thing. I'd still consider it a senseless waste of time, but it would have been readable. The problem is that it's not done beautifully. The author seems like he's obsessed with tossing in every flitting idea that crosses his transom and creating endless races of people, each of which is given a cursory mention and we move on. It was pointless because none of it stood out, and nothing was memorable or even interesting, nor did it contribute a single thing to the story unless endlessly-waffling confusion was actually the author's intent.
I quickly tired of this and gave up after a hundred pages or so. I have better things to do with my time than read another author's listing of all the alien species he thought up, but had never found a novel to fit them into so he decided to use this one as his waste disposal unit. This is the third Brin I've tried to read. The first, Kiln People, I read a long time ago and really enjoyed, but the last one, and now this I have not, so I guess I'm done with this author now. I can't commend this based on what I read of it.