Like many of Baxter's books, this is another extrapolation on scientific theories to push humanity to the limits of society. Interesting read, if not a little on the sad side. I think talking about anything else about the book will spoil it somehow. It wasn't my favorite of Baxter's books (probably that would still be something on the Manifold series, probably Manifold: Time, but that's debatable. Like many other things, it's hard to me to talk about my favorites, as it would somehow mean that I would prefer reading it again than reading something new.
Anyway, if you like the genre, I recommend it. If you like romances or adventure with happy endings, you probably should stay away from this 490-page tome.