I've only read two of his novels, but here's what I thought, if it's of any help.
Kraken: part detective story, part gangster thriller, part black comedy, part exploration of cults and belief. I had difficulty getting into it as although the writing was good, the plot, which mixes eschatology, demonic East End villains, the theft of a preserved giant squid from the National History Museum and the worship of said squid (it's a god), was too surreal for me, and the characters too weird, and after a couple of dozen pages I was hoping everyone would soon keel over and die from a surfeit of deep-fried calamari. It continued weird to the very last page with memory-angels made of bones and bottles, folding people, talking tattoos, sentient ink, squid worship, an embassy of – and filled with – the sea, literal knuckleheads, a trade union for familiars, and phasers never set to stun. Wildly, exuberantly, creative, but not a work I could say I enjoyed.
The City and the City: this was very different from the squiddy wordiness of Kraken, and I liked the matter-of-factness and decency of the first person narrator – a police inspector in a fractured vaguely East European city investigating a murder. The constant teasers in the opening chapters regarding the other city which physically occupies much the same space became a bit irritating, and I was annoyed Mieville never bothered to explain how the situation developed, nor how something called the Breach was funded, nor what all the Precursor stuff was about (the city and people who originally occupied the entirety of the now-divided land), plus Mieville's politics made it obvious who some of the baddies were going to be, but overall I enjoyed it.
I've also read a collection of his short stories, but I can't now recall anything of the book beyond a deep dislike of everything in it.
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