Full disclosure: I am a Tufte fanboy. I want everyone to read Tufte. Of all my book collection, I think they might be the ones I'd save first from a raging fire.
If you're familiar with Tufte's previous books, which have something of a 'handbook' feel to them, this one is a more erudite, extra-disciplinary, philosophical extension. The ground is less familiar, less quantitative, ranging more freely into other fields, especially the visual arts.
If you're not familiar with Tufte, this might or might not be the book to start with. If you're interested in his work on information design and the presentation of data, I would suggest perhaps not starting here. Buy Envisioning Information or Visual Explanations first. But if you're interested in his work as a sculptor or his views as an art critic, this is the one for you. If you're interested in book design and typography, or just want to read something original and thought-provoking, any of Tufte's books will fit the bill equally well.
Second thoughts, whoever you are, just buy this book and lose yourself in Tufte's beautiful world.