This is the best SF book I've read in some time. I'm surprised to see it getting so little, and at times undeservedly negative, attention from reviewers on here.
"In the Mouth of the Whale" introduces a much wider range of elements compared to the first two novels in the Quiet War series-- which basically expounded a near-ish future history of solar system colonisation, with oodles of loving descriptions of habitat designs/ecosystem engineering. Here there are stronger characters, a much stronger narrative thread (in fact three of them, initially), some refreshingly different settings-- including a gas giant and various virtual environments, besides the obligatory hollowed out asteroids-- some stunningly good descriptive passages, and a real sense of the author starting to get solidly to grips with some substantive, timeless, human themes. Tyranny, love, the extent to which we have control over our destiny, you know the kind of thing. It's not that this stuff was absent from the earlier novels, just that it's explored with a surer hand in this one. Although the book describes a much altered and splintered version of far future humanity in the unfamiliar setting of another star system, it still manages to be a thoroughly human work (The True are Us, of course). Which is not to say that it's lacking in either hard science-y stuff, or some decent action sequences (indeed, one criticism of the Quiet War might be that it was too quiet- but with the one exception mentioned below, that's not a problem here).
It's true that there are echoes from other SF authors-- gas giant-based intelligence, virtual hells and the cryptosphere-like Library were bittersweet reminders of Iain M. Banks-- and the cyberspace stuff has of course been done thoroughly elsewhere, while other passages call to mind Alistair Reynolds and Kim Stanley Robinson. In lesser hands, these echoes might make the book feel derivative, but the quality of the writing is such that these reminders are rather pleasing. It's like hearing snatches of your favourite music on a radio programme which, in itself, happens to be rather good. Somehow it all adds up to something more than the sum of its parts. If I've got one small niggle, it's the amount of time spent on Sri's early life, not all of which serves to move either the character or the story along. But that's not enough to lose this book its amply deserved five stars.
So- ignore the naysayers. Read it and enjoy. Just don't expect it to be like the other books in the series. Expect it to be more.