The book consists of seven interlocking stories, three historical, one contemporary, and two SF. Each one is written in a different style, which you might call a pastiche. The historical genre voices are 19th century nautical, 1930s aesthetic and 1970s action/conspiracy. The contemporary voice is the alienated dissociated things-fall-apart style.
It is interesting to read two SF pastiches, as I think a typical literary author would attempt no more than one. It shows a confidence and understanding of the genre. Edblog suggested, when he read the book, that these two sections were the least successful. However they are not the glib attempts of a literary type working in a genre he despises. Otherwise I would have cast it aside with a curse.
The first SF section is techno-futuristic, with clones, hover cars and the like. Like cyberpunk it is liberally spattered with brand names, and like Cordwainer Smith it centres on a doe-like martyred hero of the underclass. The second SF is post-apocalyptic rustic, with Ridley-Walker style language, and a Ursula Le Guin style of anthropology. So, the guy knows his SF. These stories probably don't add anything much to the authors he borrows from, except embedding them in this trans-genre context, which perhaps illuminates them in a new way.
Incidentally the novel that the overall structure most resembles is Years of Rice and Salt by Kim Stanley Robinson, so that's at least five SF styles being utilised here.
None of the sections, the SF included, is ground-breaking in itself, nor is the over-arching concept, and the whole is not an earth-shattering book, but it is one of the most enjoyable books I have read in several months. To be honest I haven't enjoyed much new stuff lately and I hope this breaks my reading drought. I will definitely read the other novels by David Mitchell.
Incidentally coalescent wonders here whether the barrier between SF and the rest of literature is breaking down and whether this is a good or a bad thing. In my opinion it's got to be a good thing, but raises the danger that SF starts to be judged by literary standards (characterisation and language) to the neglect of our special genre standards (such as originality, awe and challenge).