Well. That was unexpected. "Cloud Atlas" is an astonishingly original work of fiction with strong science fiction overtones, the kind of book that doesn't usually do so well with the general populace. And yet it has been incredibly popular, and even had a movie made out of it (which seems improbably difficult a task, and I'll have to see it just to see how on earth they managed it). It took me a while to warm up to the book, but now I love it. The structure reminds me a bit of "2312" by Kim Stanley Robinson: each section ends or starts abruptly, so we rarely get the whole story all in one go, and the reader is left trying to put together the pieces.
The first bit reminds me of "The Thousand Autumns of Jacob de Zoet," Mitchell's other book that I've read and loved. What is so extraordinary about this work is how effortlessly Mitchell steps into different voices. Most authors have a distinctive style and vocabulary, but Mitchell has thrown that out the window and actually succeeded in writing parts of the book that could have easily come from different authors, indeed creating his own dialect on more than one occasion.
It took me a good long while to pierce through to the message(s) behind this story. It seems to me they are twofold. First, the obvious commentary on human rapacity leading to eventual world destruction. We get this most strongly in the central pieces, which take place in the future, and a bleak future it is indeed. Second, the less obvious and complicatedly explained idea of pages 392-3: "Our model of time: an infinite matryoshka doll of painted moments, each 'shell' (the present) encased inside a nest of 'shells' (previous presents)..." Posited in a different way: My reality is real to me. It is, indeed, the most real thing in the world. Your reality is only a story to me, one you tell to me, so that your story can only be taken on the face value you present it with, thus it is not real. It is "virtual." The things you tell me you have done may or may not be true, and therefore cannot be considered reality, not in the way my own life is real to me. We are all just stories to someone else, no matter how real our lives seem to ourselves. And the past is just another story, another less-real reality.
In conclusion, David Mitchell = wow. What more can be said?