Absolutely terrific. This is the kind of richly imagined, luscious prose that makes me want to quit my job and write. Mieville is incredibly good at pacing and drive; it's not often I'm told I'm reading with my mouth hanging open. 
 As a re-imagining of Moby Dick, it's remarkably clever--it manages to capture elements of Melville's epic (which, admittedly, I have hated with a passion my whole life) and still seem fresh and new and entirely unique. 
 One of those rare books you read and wonder where the hell the author came up with their ideas--not that it matters, because the result is just deliciously good.