I've just finished reading — and thoroughly enjoying — Transition by Iain Banks. Despite a terrible writeup in the Guardian, I found the book to concentrate just as strongly on character as world-building, but I wouldn't be surprised if a sequel was on the cards.
The novel is, in part, an exploration of the many worlds theory of quantum mechanics. Or at least that's it's setting. In the UK, it has been published without the traditional 'M' infix denoting Science Fiction, although it is undeniably so: It's not even pretending to be anything else.
The book reminded me of Quarantine, and to a lesser extend Permutation City, both by Greg Egan; and another book I've read recently which I can't reveal without spoiling this one.