Redemption Ark is the sequel to 'Revelation Space' and the second book in the Revelation Space trilogy. There are actually five books in the Revelation Space universe, but the other two are standalone novels that don't add substantially to the overall story arc. So if you haven't already, start with Revelation Space. You could read this book on its own, but you'll get a lot more from it if you read them in order.
Humanity is teetering on the brink. The Inhibitors have been awoken, and their cold machine sentience starts the process of wiping out the human race. They've sanitized the galaxy of intelligent life countless times before in the billions of years since their creation, and they will do it countless times again. Can anything stop them?
This book, as with Reynolds other books, is part space opera and part Hard SF. It is set a few years after the events of Revelation Space; there are some overlapping characters, but a cast of new characters as well. The story starts slowly, and the first quarter of the book takes time setting the scene, introducing new characters and backplot. The last 10-15% of the book is also quite rushed, almost as much happens in the epilogue as in the rest of the book. Still, these are minor points in what was an extremely good book. It's got great characters it is easy to care about, a cracking plot and a real sense of wonder about it.
I'm really starting to like Alastair Reynolds stuff, after just two books and one short story. Inevitable comparisons can be made to Peter F Hamilton's epic space operas. Reynolds books, so far at least, are darker and a bit stranger along with being more tightly focused. Each book seems to be focused on at most several sets of characters. Peter F Hamilton, in contrast, fills his books with countless different groups of characters on many diverse worlds. Given the effective lack of faster than light travel/communication in Reynolds book, it is always going to be this way. It does make Alastair Reynolds books easier to keep up with and remember what is going on!
Overall I'm giving this book 8/10. Not perfect by any means, but pretty damn good nonetheless. Roll on Absolution Gap (book 3/3 in the trilogy).