Joshua, I may well have said that if it didn't grab you in the first few chapters, it wasn't for you. Apparently I was wrong

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For me, although the slakemoth plot was riveting, it was really the language and the richness of the world that made me love the novel so much. You start to see the richness within the first few chapters, and you see the language from the first page. I figured folks would either love it or hate it for these reasons.
The politics in the bok didn't bother me at all. Not because I'm a leftist, but because he was describing plausible scenes. The culture was, after all, loosely based on Victorian England, in a society massively moving into industrialization; riots like the ones in the book were definitely occurrences in England (and indeed throughout Europe and the US) during the analogous period. An author who write a society-based book about such a society and DOESN'T include labor riots would be making a more political decision than an author who DOES include labor riots, IMO.
Indeed, although my favorite scenes in the book revolved around the slakemoths, besides those my favorite scene was the labor riot. The growing tension as the riot moves forward, the cautious optimism on the part of the strikers -- and then the utter horror of Giant Freakin Floating Jellyfish moving through the streets maiming and killing people. Gaaah! Very cool stuff.
I definitely got a feel of different cultures from the nonhumans: the beetleheads had their strange hivemind, the birdmen were sort of savage utopian anarchists, the cactaceae were ultra-traditionalist xenophobes. Other than the cactaceae, I'd say that the nonhuman cultures were
predicated on being nonhuman: there's no way that humans could have a culture like the beetleheads' or like the birdmen's.
It may help that when I read the book, the only "hype" I'd heard was a recommendation in
The Year's Best Fantasy and Horror. I went into it expecting a good read, but was completely blon away by what I encountered. I only found out about Mieville's other work, about his biography, and about his critical acclaim after I'd finished reading
PSS. I'm pretty glad I was able to read the book like this; I can definitely see how the hype around him could make the book less absorbing.
Glad you more-or-less liked it, anyway -- as I've said before, it's IMO the best fantasy I've read in years!
Daniel