The film adaptation opens tomorrow and it's unlikely that I'll ever see it. The trailer makes the film look quite insufferable, Hollywoodizing the novel by inventing a romantic aspect and using a "reincarnation" idea so that the filmmakers can indulge in a bit of stunt casting. I could be wrong of course but even if those details are off it's hard to imagine the result will be worthwhile in any way at all.
Then again the book is something of a mixed bag. As you've probably heard it's a series of nestled stories where the first and last are the same, the second and next-to-last another, etc. Each one has a reference to the previous in some way and there are a few hints of a connection such as a distinctive birthmark that the main characters share. The stories are also genre pieces such as historical fiction, thriller, SF and so on.
Clever, right? Well yes and actually written with a knack for the styles that keeps it from getting too tedious. Except for the SF parts where the book goes completely off the rails and becomes nearly unreadable. This highlights the main issue (I wouldn't go so far as to call it a problem) that these are really very loosely connected short stories and only a novel in the broadest sense. This seems to be a small trend recently with other books such as The Imperfectionists and Welcome to the Goon Squad also being fix-ups as old-school SF people used to call this. In fact Cloud Atlas is similar in many ways to Welcome to the Goon Squad though while Egan made more of a novel out of her subject she was also note remotely skilled enough to pull off what she was trying to do. (It's also worth noting that Egan has only a mainstream lit-type's understanding of SF - basically that it's only predictions - so her SF section is ridiculous but Mitchell at least uses two distinct and genuine styles of SF. Quite poorly admittedly but it's an honest attempt.)
Mitchell seems to be basing his stories on the idea of employer/employee (or master/slave in a couple of cases) relationships which the film seems to have turned into more a romance. The problem is that I'm actually not quite sure that's what Mitchell was doing or even if he intended for there to be any thematic connection. Which is another reason that in the end the book is a slapdash affair that pushes some plodding material up against the good stuff. And when it's good it's good enough that I suspect other Mitchell novels are worth checking out. (Particularly I like the end of the first part in a way that can only happen in a printed book - an ebook can only hint at how that works.)