Pixar's The Art of.... books tend to be wildly uneven in their quality. Some of them contain great insight into the creative process and clearly establish an artistic narrative that takes you from early sketchwork to final product. Othes seem almost slapdash, as if the authors had only minimal access to artwork -- and even then, only to a few artists.
The Art of WALL*E is one of the better ones. The text is excellent. Wall*E was a film whose genesis was as much in Charlie Chaplin silent films of the 1920s as it was in the ideas of Pixar's directors and producers. Unlike some films, where story drove the art, Wall*E -- by its heavy reliance on mime -- required art and story to go hand-in-hand from the very first. The text clearly brings this out, and provides real insight into how the artwork developed the way it did.
Subsequently, the artwork you get in this book is top-notch. The reader gets everything from character sketches to storyboards to unused plot lines and never-seen major characters. Seeing how art drove story, and story drove art, is the real key to Wall*E, and this book brings that out wonderfully.
My one criticism is that I wish the book wasn't as repetitive. While readers clearly are interested in Wall*E and Eve, and want to see how these characters developed over time into their final forms, I wish that there had been more about how the film developed in other ways. How did they come up with the character of Moe, and how did that character develop? How were the interiors of the Axiom conceived and reworked? How did they come to integrate live-action into the film? You won't get much of this in the book, and I think that's a shortcoming.