The Scar by China Mieville, 2002.
Very good, showing an author that succeeds at basically everything they're aiming for, and is aiming for the right things.
I've come to Mieville in just about backward order, based on local availability form different libraries. So, the order ran Iron Council, The City & the City, Un Lun Dun, now The Scar, and will conclude with Perdido Street Station and King Rat. And I am going to read them all, Mieville is a strong enough writer to merit the attention.
He's one of the truly great worldbuildings, on the level of Vance or Le Guin. Casual little details are thrown in that make for an very compelling and believable setting. Economy, politics and daily life appear clearly, this isn't just a background with a convincing set of dynasties but one that feels inhabited by a whole order of classes. Mieville is the other type of urban fantasy writer--rather than take the existing world and put a slice of the fantastic over it he weaves a fictional city in great detail. Moreover, in the Scar this city is Armada, multiple levels of pirate ships on the water, the whole structure slowly drifting across the globe. Multiple species, a giant mythological beast to pull it, yet the structures of internal trade and partisan politics are comprehensible.
This book has as well wonderful moral complexity, a rich cast with a range of attitudes and desires. As a revealing incident, at one point major plot emerges from the vampire overlord of part of Armada launching an attempted coup of the city, aligned with Eldritch sea monsters. He's an antagonist, but rendered sympathetically, along with much of the cast. The one faction in this novel shown as monstrous is also the one with the most banal focus, the city aiming at strategic transit and commerce.
A very effective and unique work.
Similar to and better than: Jack Vance's Blue World
Similar to and worse than: David Mitchell's Cloud Atlas. Not particularly similar, mind you, but the ocean-centered segments are broadly comparable.