The Bone Clocks is the next World Fantasy Award nominee I've read, and to say it's my favorite is at this point too faint praise. David Mitchell is more famous at this point for Cloud Atlas, so at some point I'd like to read that too--but for now, savoring this one is just fine.
Like Cloud Atlas, The Bone Clocks is an interconnected set of stories that spans many years. This seems to be Mitchell's main claim to fame--that he can pull so many threads together. I find it ambitious but not that unusual. And the speculative element of the book--dueling secret societies of immortals, with the afterlife explained--is somewhat conventional.
What's special about the book is how strong each section of the story is. They all develop interesting and complex characters. Both heroes and villains are (mostly) three-dimensional characters with multiple motivations. They are not easy on themselves. The spacing in time gives the story-made-of-stories a natural depth.
I don't want to summarize the plot here because it's fairly simple and a summary would give too much away. So I'll just highly recommend the book for the way the characters bring out the best in the plot. Four stars from me.