The world-building is fantastic, the characters are flawed and believable, and there are cities on wheels. Oh yes.
A very nitpicky grumble, but Reeve likes to drop in references to current pop culture, which can sometimes seem a little forced. More often, though, it's fun to go 'oh hey, I see what you did there!' Some of the references are very British (Tunbridge Wheels, anyone?) but like I say, I'm being very nitpicky here.
'Mortal Engines' takes place in the far future of Earth. The Sixty Minute War, the consequence of an out-of-control nuclear arms race, has devastated the planet and destroyed much of human civilisation. What's left is Municipal Darwinism: travelling towns and cities roaming the wastelands, searching for prey to feed their engines.
It's the only life young Tom Natsworthy has ever known, so when a chance encounter in London's Engine District sends him tumbling to (horror of horrors) the bare ground, he clings to the only thing he can: the mysterious Hester Shaw, with her scarred face and her burning desire to kill London's Head Historian. Their headlong pursuit of London leads them through the terrors of the Hunting Ground, the clawed embrace of Hester's Stalker-guardian, Shrike, and the machinations of the Anti-Traction League, to the top tier of London itself where they must face the unknown threat of MEDUSA.
I love this book, as you may have gathered from my pitiful attempt at the 'cons' section. The world-building is, quite simply, beautiful. Stark and dystopian and just a little bit terrifying, but beyond all, beautiful. It's so very, very detailed and textured that the whole setting is utterly convincing, on a level very few SF/F books manage. The Sixty Minute War, which is supposed to take place in our near future, has left technology at a very interesting level, a sort of blend of steam- and cyberpunk, with airships sailing the Bird Roads, and the mysterious fragments of Old Tech that have been salvaged from the Hunting Grounds - bits of computers that people in Tom's time barely understand (not that this stops them trying to harness them for their own devices, obviously). It was my first introduction to the idea of steampunk, before I ever knew such a genre existed, and I don't think anything I've read since has ever lived up to it.
I've already mentioned the world-building. Next, the characters. Now, I should mention this is a YA book, so it's not surprising its two protagonists, Tom and Hester, are in their mid-teens when the book starts. But. If you're sick of whiny teenaged protagonists in your fantasy, don't turn away now! Because Tom and Hester are awesome. They're not perfect, they screw things up, they don't always take the time to think things through like adults, because they act like teenagers. Well, duh, you may be thinking, but I've noticed that writers have a tendency to either make teenaged characters super-perfect, and yet tragic and Deeply Misunderstood, or else adults by another name. I think Philip Reeve writes them true, which is something he seems to do pretty consistently in all his books. Also, do you know how excited I was to find a YA heroine who isn't stunningly beautiful and a hero who isn't secretly an Adonis under his Clark Kent exterior?
The structure is that of an adventure/mystery story. It starts off with Tom and Hester just trying to get back to London, Tom to return to his life, Hester to finish the job she started, but it spirals into something much bigger - the mysterious MEDUSA artefact that could (say it with me now) destroy the world. Only, of course, the point is that Tom and Hester don't know that, so a good part of the book is devoted to them figuring out just what in Quirke's name is going on. That said, there's never much sitting round, running through hypotheses. No, there's too much being chased by airpirates, escaping from Stalkers, and stealing airships for that.
I flew through this book - the pace is well-judged - break-neck at just the right points, slow and measured (well, slower) at others. It was a joy to read (for about the fourth time) and I'm making my way through the rest of the quartet at the moment. I hear there are prequels, too...