A massive 70+ page Extras chapter features Achievements & Trophies, Secrets, a full interpretation of the original Assassin's Creed and Assassin's Creed II game narratives, an in-depth developer Behind-the-Scenes with exclusive interviews from the game's creators as well as an art section packed with images direct from the team. The Super-visual Walkthrough with area maps details mandatory action on the left-hand page and advanced data & secrets on the right. A complete Reference & Analysis chapter covers special moves, weapons, equipment, items, shops, enemies and missions.
I didn't use the walkthrough at all, but for getting extras like the feathers and trophies, this book is very helpful. At the back there are interviews with the dev team that explains the (confusing) ending to the game more clearly.