In my opinion, this book is a must-have if you enjoy the Percy Jackson book series. My review of this book assumes that the reader is already familiar with the series.
The book is divided into eight sections: Percy Jackson, Life at Camp, Gods & Spirits, Percy Jackson's Bestiary, The Labyrinth, The Underworld, The Storehouse of the Gods, and Compendium.
The first section covers everything you've ever wanted to know about Percy, including information about his mom, Sally; his stepfather, Gabe Ugliano; Percy's problems at all the schools he's attended; the Fates; and the Furies. There's even a copy of one of Percy's report cards.
Section two is all about Camp Half-Blood. There's a detailed map and a colour painting of the campers' cabins; a 'Meet the Campers' piece; a piece on 'The Truth about Mr. Brunner;' and a rundown on other characters at camp (Argus, the Oracle, etc.) Interspersed throughout this section are fun things like 'Ten Signs That You May Be a Half-Blood,' 'Detect a Satyr,' a copy of Percy's activity schedule while at camp, a quiz to figure out who your godly parent is (if you think you might be a half-blood), and information on centaurs, pegasi, and cyclopes.
Section three begins with the story of Kronos and gives information on Zeus and his brothers, and the children of the 'Big 3' gods (Zeus, Poseidon, and Hades). From there, you get to read detailed biographies of Zeus, Poseidon, Ares, Athena, and an assortment of slightly lesser gods and goddesses. There are modern colour 'paintings' of Zeus, Poseidon, Ares, Athena, Hestia, and Hephaestus (envisioning them as they appear in the books); other gods & goddesses appear in photos of actual classical artworks: marble busts, bas-relief sculptures, statues. Included in this section is 'Chiron's Guide to Who's Who in Greek Mythology,' a piece on minor gods & spirits (the Charites, the Muses, etc.), a piece on lesser gods of the sea, and some detailed information on minor deities like Adonis, Nemesis, etc.
Section four contains the Bestiary - a detailed rundown of every monster Percy meets in the books. Includes colour 'paintings' showing some of the creatures as envisioned for the books, and photos of actual classical artworks of other monsters.
Section five covers the quest in the Labyrinth from the fourth book in the series, The Battle of the Labyrinth. It's quite a short section, but it also has an interesting piece on the history of Alcatraz prison, and a beautiful colour painting of how Daedalus' workshop might have looked to Percy.
Section six, The Underworld, is another short section. It features 'A Guided Tour of the Underworld,' written by Nico di Angelo as if he were a tour guide.
Section seven, The Storehouse of the Gods, begins with a detailed look at a lot of the items, weapons, and useful trinkets given to, or encountered by, Percy and his friends in their adventures - some cool photos of actual items here, including Thalia's magical bracelet Aegis, Annabeth's invisibility cap, Luke's sword Backbiter, dinosaur teeth, golden drachmas, and the winged shoes that Luke gives Percy. Also included is information on all of the Automata encountered by Percy: the Colchis Bulls, the Guardians, the Skeleton Warriors, etc.
Section eight, the Compendium, provides information on some of the minor characters mentioned in the books: Rachel Elizabeth Dare, Annabeth's father Dr. Chase, the god Pan, Atlas, etc.
This entire book was written in a very engaging and witty style throughout, perfect for the 9 - 12 age group; and the frequent inclusion of diversions like trivia, quizzes, photos, etc. also ensures that the younger reader is never bombarded with just written information. Adult readers will gain just as much from this book as kids will.
Additional coolness factors for this book come in the form of a lenticular photo strip across the front cover that changes as you tilt the book (one set of photos is Percy, Poseidon, Ares, and Zeus; the other set is Kampe, Morpheus, Grover, and Athena) and an included 9-card set of mini trading cards that gives the lowdown on some of the series' characters (Percy, Luke, Annabeth, Poseidon, etc.) Glued inside the front cover is a 9-tier pocket to keep the cards in. The book itself closes securely with a magnetic flap.