A good Mieville is always a treat, and Embassytown is very good Mieville.
(Not quite as good as Perdido Street Station, alas, but then hardly anything is.)
It's science fiction, and reasonably hard SF at that. The eponymous Embassytown is a colony on the edge of known space, cut off from its imperial power by years of travel through the immer, the always to our fragile universe's now. Embassytown is enveloped, on sufferance, in a larger city, which is populated by the Hosts, alien beings with two mouths who speak a language that's unique in the universe because it's impossible to lie using it. Because so-called Language is spoken with two mouths at once, and because the meaning of Language doesn't lie in the sounds but in the mind that creates them, the only humans who can speak to the Hosts are the Ambassadors, clones whose minds are linked by training and technology.
Our Heroine is Avice, a traveller on the immer who's returned to her home planet with her new husband Scile, a linguist who's avid to study the Hosts' language. (Avice and Scile, incidentally, have a relationship that's by choice non-sexual, which was a nice surprise.) Avice isn't really a primary mover for most of the book - mainly she's trying to find out things, work out Embassytown politics - but she's always centrally placed by her minor celebrity as a traveller who's returned home to observe the turmoil that comes to Embassytown when a new Ambassador, sent by the imperial power, basically fucks up the Hosts' minds by speaking Language not quite right.
What Embassytown is, basically, is an SF novel with a classic pulp structure whose plot turns on linguistic theory: the idea that language signifies but doesn't refer, that it's the sound of language that's important not the intent behind it.
That's really impressive. Because Mieville makes this readable: not just readable but compelling. We don't get too much characterisation, which would be my one complaint, but honestly I think that's a function of the kind of book Mieville's trying to write rather than a specific failing, and the worldbuilding and the ideas behind it are so well-developed that I can give him a pass on that.
Add to that Mieville's usual hallmarks - the neologisms, the moral ambiguity, the carefully calculated brutality, the deflation of narrative expectation - and you get something that's bizarre and fascinating and layered and clever.
Like I said, a treat.