A very good, but hard to describe novel. Starting in a fantasy world - one that will be hilariously familiar to players of MMORPGs - we follow a chap who implies there is a lot more going on. He helps to defeat some dark priests and that leads on to crazier and crazier stuff as we get to find out what is going on.
It's not quite a post-singularity novel, but the things that have led to the world that Williams describe certainly changed things for humanity a great deal. For more detail, read the novel.