I found this book to be utterly captivating. I was enchanted from page one. Erin Morgenstern is the master of atmosphere and description, and more importantly, the atmosphere she happened to be describing punched all of my buttons in all the right ways.
The only criticism I would give this book is that it was more about the circus (and the contest) itself rather than its characters, who were merely just players in the game, most of them unwittingly. There wasn't really a plot in the usual fashion, more like an unfolding where all you get is certain pieces at a time and never in the right order, and only once the thing is completely unfurled do you see that it always looked like that, even from the very beginning. I might up my rating to a full five stars in the future, but I'm not sure how it would play on re-read, all this emphasis on setting (wonderful though it was).
Definitely recommend this to everyone, though. Worth it just for the experience of the thing. If you don't put this book down wishing the Circus was real, there is something hopelessly wrong with you.