In a word:
compelling. So much so that I neglected several Very Important Things I was to be doing with regards to my graduate school work. And if that isn't a testament to the ability of this book to suck you in (against your better judgement), then I don't know what is.
The true delight of this book is what you feel coming--you can feel the weight of the fabled Twist, that de rigeur moment where the plot flips over on itself. You often feel it coming, know it's getting nearer, and this book is no exception.
However, when the Twist does finally arrive, it has such a reverberating shock that it is dumbfounding, and delightful.
And I immediately went out and purchased
Five Quarters of the Orange, another book by Harris.