So, he writes this book with an insider's perspective. At every opportunity he makes fun of them (as only a close friend can) and spends the first part of the book tracing their career up to The Big Lebowski. The rest of the book plays out as a quasi-Making Of that is quite an entertaining read. For example, he places their film in the grand tradition of bowling noir, a very rarified subgenre of the film noir. Robertson is quite funny as he pontificates about this subgenre at some length.
If I had one complaint about the book is the amount of detail that is gone into about the storyboarding process which I could have done without. But this is a minor quibble at best.
Robertson's style of writing is very casual and easy to read--it won't take you long to get through this book. If you are a hardcore fan of the Coens, then you will definitely enjoy this book and all the little, inside jokes. It will certainly deepen your appreciation for the film and acts as a great companion-piece.