This book is basically everything that makes a Claudia Roden book -- personal stories, history, and much more -- combined with some truly beautiful Phaidonesque food photography. It's a doorstop, no question, but it's worth trying to schlep it around just to be able to browse through it. The recipes are all marked by area of origin, and are chosen to reflect each area's specialties, such as Valencia's rice, seafood from Cantabria, the Basque country, and the Balearic Islands, Asturias' apples, and Madrid's signature boiled dinner, the cocido madrileño.
The aesthetics are an important aspect of this book; while the text itself is probably about the same or slightly shorter than Roden's other books, the book as a whole was conceived as a coffee table book, with generous (and obviously Phaidon-influenced) food photography. Roden's friends who helped her with the book also get their own introductions in sidebars, along with ingredients and cultural forces that shaped Spanish food from medieval into modern times. (Roden, being Sephardic Jewish, places special emphasis on the Jewish contributions to the cuisine, and makes a special point to cover how Spain has come to appreciate centuries of contributions by Jews and Conversos.)
For a long time -- over twenty-five years now -- Penelope Casas' The Foods and Wines of Spain has been possibly the definitive book in English on Spanish food. It's still an excellent book, but in the years since Casas published her first book, Spanish food has rocketed to worldwide fame as the youngest of Europe's great national cuisines, joining French, Italian, and Greek food thanks to the efforts of both traditionalists and modernists. I don't know that I'd say Roden's book replaces Casas', but the simple fact of it being so far up to date as well as being artistically beautiful just edges out Casas as the book to buy if you're only buying one. (I own both, and I'd suggest you do too, along with 1080 Recipes, which was written in Spain for Spanish cooks, but received a very nice, slightly quirky treatment from Phaidon.) But even if you don't care about any of the above, Claudia Roden is one of the Anglophone food world's great treasures, and frankly a new book by her is really all the excuse you need.