Cloud Atlas is a set of 6 nested stories, spanning both centuries and genres. The nesting is deep enough that I'd forgotten the outermost story by the time I got back to it! It stretches from a couple of centuries ago to a post-apocalyptic future. I suppose a decaying society is needed in order to actually tie up the (middle) ending sensibly, but it's pretty dystopic!
The stories are apparently supposed to be interlinked, with the main characters connected by some form of reincarnation, but I found this lost beneath the differences between the stories. I think the author was trying to demonstrate the range of styles they can deal with, but with the differences more obvious than the similarities, I found it something like the Enigma variations! I think there is some theme running through it, but it's a little bit subtle for me. The ending seems to try to tie it into something about human nature and selfishness, but, well... it didn't really click for me.
It's a fun concept, and reasonably well-executed. Interesting and varied stories, even if they're individually derivative and predictable. I'm not sure sure if any bigger plans the author had work, but it's at least nicely diverting.