Much like Perdido Street Station
in general style, and I enjoyed
it greatly for all the same reasons: if you described the setting out of
context then it'd obviously be completely ridiculous (our protagonist
starts by being press-ganged into being a pirate librarian), but it's
played straight, and the worldbuilding and characterisation all hangs
together nicely.
The result is a world that I don't so much want another story about as a
holiday to.
Highly recommended.
ISBN 0330534319.