This is a thoroughly enjoyable book. It's not flawless; and I'll address those (minor) quibbles at the end of this review, but it's nearly flawless, and certainly deserving of five stars. I'd like to start, however, by stating again how much fun this book is. There's a lot of stuff here, and it's all well done. The characters are fun, the action is good, the adventure is, well, adventuresome, and the conspiracy, once it all comes into place, is absolutely brilliant. Young doesn't cheat, either. Small clues are given throughout, and it all leads up to a rather satisfying villainous reveal. That's another thing this book has in its favor. The villain is very, very smart, and does not do evil things for the sake of evil, or with only flimsy justification, which is nice to see, considering how easily a book with this kind of plot could have slipped into that territory.
The thing this book does best, however, is dialogue. It's witty, memorable and it really helps to give each character a unique feel. I cannot say enough how pleased I am with the conversations these characters have with each other, and how much fun they were to read.
The only quibble I really have has to do with description. Some (very small) parts feel a bit rushed, not due to issues of pacing (which is quite well done,) but due to a lack of description, or rushed description. Unfortunatly, the best examples are also spoilers, so I don't really want to put them here. I'd like to emphasize though, that these are few and far between, and that I can think of only three small instances offhand. Still, they struck he as important enough to be worth mentioning in this review.
On the whole, this book is quite excellent, and I've been recommending it to my friends and family since I picked it up yesterday. The small issues mentioned above do not diminish from my enjoyment of it in any meaningful way, and it does deserve five stars.