I enjoyed this, but it is too long, and too derivative. As I said reviewing Something Coming Through: read 400 Billion Stars instead.
Of course, being long is good if you want something to fill in time; which I rather did; so that's not a good complaint. However, the material does perhaps get stretched thin, and the bits that McAuley doesn't have a good back story for become a bit too obvious, instead of staying only glimpsed.
If you follow the obvious reviews, you'll see people noticing the obvious debt to Gene Wolfe's Book of the New Sun; and indeed the much less successful Long Sun series. Apart from the obvious stuff, which is so obvious that I tend to think it was intended to be noticed, there are more subtle hints for the cognoscenti, like one of the minor characters being called Azoth.
The overall cycle - stop reading me here if you have any intent to read the book - is like Wolfe; in the way that it carefully constructs a circle in time; though McAuley's circle is heavy and clumsy compared to Wolfe. The shrines and avatars are blatantly Wolfe.
The return of one spaceship after millions of years is very much in the line of Across Realtime (which, if you haven't read it, should be on your must-read list along with A Fire Upon the Deep). As is the idea of a group of rather lost "people" left wondering "WTF happened?" after everyone else Transcended. In Realtime this is neatly handled by not being handled at all; in Confluence it is constantly alluded to by the Eye of the Preservers and so on; but after a while it becomes clear that it will never become clear and he really has nothing to say about the subject.
There are some terribly odd bits of physics. A simple illustration is that the Prefect's energy pistol has three shots, then needs a day in the sunshine. But that wouldn't be close to enough (OTOH the weird knife that likes being stuck in fires is nice). A more complex one is the way the sun rises then sets, by the whole world tilting then tilting back. In terms of conservation of momentum that's insane, even to someone who has allowed themselves arbitrary gravity manipulation.
However, all that is balanced by a decently told story. Some portions struggle for a kind of eloquence: the idea of Yama "freeing" the indigenes with his blood is nice, as long as you don't stop and think "hold on, what's the point? If that was the point, why not do it a million years ago?"