This is the sort of space opera I can love. Forget Alastair Reynolds' Revelation Space trilogy, with its sloppy (sometimes indulgent) writing and wooden characters; forget Iain M. Banks' Culture novels, with their climaxes that lead to nothing but futility; forget even Lois McMaster Bujold's Vorkosigan Saga -- much though I love the characters and the wit, it doesn't have the breadth of imagination or the sheer scope that Westerfeld captures here.
The Risen Empire stars with a bang, throwing the reader into the action head-first in the perspective of a pilot on a desperate reconnoissance mission a couple hours after the Child Empress has been taken hostage. It shifts perspective every few pages, always clearly marked in the book and with enough clues in the first paragraph for the reader to settle into the new perspective seemlessly, and every time the perspective shifts it adds to the tension. As in any great space opera, there is a lot going on -- enemies without and within, unlikely characters thrown together and forced to forge a bond, people you can root for (but, rarer in space opera, no villains -- Westerfeld wisely shows the reader the Rix side of the action as well, and even the Emperor is crafted with an eye towards the sort of real motivations that might drive a person to do horrible things).
But of course, no book can maintain that sort of frenetic pace for 300+ pages, and it is actually the slower moments that hold this story's heart. After reaching a breaking point in the battle, it jumps back in time to show us the meeting between Zai and his lover Oxham, called the Mad Senator for reasons I won't spoil (but which I love). Their relationship grows quickly in book-time but is drawn out over the course of the novel in slow, luxuriant snippets for the reader. Oxham is a wonderful character, fully as complex as Zai (and their relationship is hardly as easy as most writers would make it -- they're separated by some pretty strong philosophical differences), and once she is introduced her present-time storyline is just as compelling as the space battle her lover is leading -- political wrangling, after all, is at least as dangerous an occupation as starship captaining, and the stakes are higher because mistakes are always taken out in innocent blood.
And just as obviously (well, at least to me, though given how many books I read that simply consist of grim men doing grim things maybe it isn't as obvious to everyone else) Westerfeld finds ways of sneaking in a fair amount of levity. The Emperor's undead cats, Oxham's House, and Alexander were all delightful elements that I won't spoil by explaining here. The entire novel was pitch-perfect, shifting between actions with dire consequences and moments of sheer absurdity with a wonderfully light touch.
It does have a couple flaws: though I prefer it to Banks' Culture novels, Banks is a far superior stylist -- Westerfeld's prose succeeds in getting out of the way of the story admirably, but it doesn't soar; there were a couple of (very minor) elements that took me out of the story because they struck me as anachronisms (a reference to a wax museum? really?); and it is very much a part one -- Westerfeld intended this volume and the second volume (The Killing of Worlds) to be one novel titled Succession, but it ended up being a little too long to publish in one volume economically, so it got split in half (meaning you had better have the second volume handy when you finish this one -- it definitely has a cliffhanger ending). But overall, this is a great book, exactly the sort of book I read science fiction for.
I think that objectively, this was a better book than his "Specials" series, but somehow, it just didn't grab me emotionally. I'm still going to read the sequel, since I already have it.
The 80 worlds of human domain is ran by an Emperor who is immortal, but now human-augmented AI (artifical intelegence) is threatening to destroy all know worlds. This is a fight to the end.