Mitchell is easily one of my favorite authors. The man is brilliant. Cloud Atlas is definitely one of my favorite books, and probably my favorite by him. (I promise not to say 'favorite' again in this post..

) Of the three I have read, I liked Black Swan Green least, though I did think it was a perfect seamless whole. Very creative and well written. It is definitely his most "simple" novel, following one character, and probably the most universally accessible. Deep down, however, it is littered with very nice subtlety. I've heard it called the "English" Catcher in the rye. Number 9 Dream is not as accessible, but just as, if not more, brilliant, and an incredibly fun read. I found myself laughing out loud, and sitting wide eyed at his wit and profound insight into the complexities of human interaction. I haven't read ghostwritten yet, though I've heard great things. Highly recommend all of Mitchell. Love him. Exhausted his opportunities? You mean as an author? I think that David Mitchell is a man of limitless potential, talent, and opportunity.
(Very short summary of major awards: Ghostwritten won the John Llewellyn Rhys Prize ((for best work of British literature written by an author under 35)) and was shortlisted for the Guardian First Book Award. His two subsequent novels, number9dream ((2001)) and Cloud Atlas ((2004)), were both shortlisted for the Man Booker Prize. In 2003, he was selected as one of Granta’s Best of Young British Novelists. Cloud Atlas was also nominated for the 2004 Nebula Award for Best Novel, and won the British Book Award Literary Fiction Award and the Richard & Judy Book of the Year award. Just a short list from a glance at wikipedia.)
Or did you mean Black swan green was exhausted :-X? Hyland is great, too, for sure.