Like Ghostwritten and The Bone Clocks, this is fundamentally a series of novellas that have been threaded together into a novel. The biggest way you notice this is the structure: you get six intriguing openings, and then the payoff to each in reverse order. This will be an issue for some, as, up until the half way point, the book is starting over every fifty pages. New setting, new characters, new narrator, and no overarching plot. 
 To me this was a delight, but I fully admit it's because I love Mitchell's style. His prose is beautiful and his grasp of narrative voice is expert, so I would happily read a dozen of his novel openings in quick succession. But it's never a comfortable read, you never have that easy middle section of the book where you know who the major characters are, and see roughly where the plot is going. You always have to concentrate. The payoff, of course, is that the back half of the novel is like freewheeling down the other side of the hill. Ending, after ending, after ending. 
 This strength is also a potential drawback. We jump from dense historical fiction filled with arcane terminology, to a thriller, to a Kafkaesque satire, to a SF dystopia. I would happily read any of those books, and am happy to read them threaded together, but I can also understand why readers might be turned off. Some characters and voices are more engaging than others (Adam Ewing sailing around the Pacific did not do much for this writer, I must confess), and they are all limited in how far they can grow because each protagonist only has ninety pages to stretch his or her wings. So if you like novels with deep, expansive character work, you will be short-changed here. 
 What really holds this together though, in my opinion, is the way this structure, and the overarching themes (exploitation and the nature of power, civilisation and "barbarism") reflect and build upon each other. For example, the "thriller" novella shows a very believable modern-day company playing fast and loose with its employee's lives in order to make money; we later jump to a future dystopia run by an entire government of such companies, where the earlier seeds are taken to logical extremes. This sort of conceptual connection runs throughout. 
 Structurally, these Russian Doll novellas start in a primitive past, move forward through history (and of course technological development), to a future point of apocalypse where we have all become "savages" once again. Then it pulls back out and shows this all in reverse. The effect is an endless, mirroring cycle of rise and fall, and that's what gives this fragmented storytelling real heft.