This is a quite satisfying conclusion to this epic pioneer hard SF tale of many Earths. :) With a sideline of many many cosmos, too. :) 
 I'm really glad I got to read all five books, and I didn't even get very misty-eyed by the thought that Mr. Baxter had to finish this without Sir Terry. The manuscripts had been penned long before his death, so the core story and practically everything else is as he'd have wished it. 
 I can see that, too. All those plot threads and hints get tied up in a very cool way, with some of the more interesting Earths explored deeply, one-on-one with Joshua and his troll friends, all the way to the end where a Contact-like exploration of the galaxy ensues. :) With multi-galaxy benefits, of course. 
 The whole concept is very intelligence-friendly. This isn't a universe that doesn't reward consciousness and intelligence. Indeed, things are set up quite nicely to help everyone along that path. Imagination has its rewards. :) 
 More than anything, these are very optimistic books. I've been missing that in my reading diet. :) 
 So glad this exists. :)