This is a fairly complete collection of game mastery advice, and unlike most game master's guides, completely unnecessary for play. But oh so worth it!

Castles & Crusades came out a few years after the D20 open game license came about. The team took that open reference and took a step back, making a game quite like 1978's Advanced Dungeons and Dragons. In that game, the Dungeon Master's Guide contained all the needed charts for combat, conditions and treasure - a required resource for game play. Castles & Crusades used the D20 model and encapsulated all that in the basic rules - no lookup charts required. In fact, for more than five years, Castles & Crusades consisted of only a player manual and the book Monsters & Treasure.

The Castle Keeper's Guide collected the extra bits, from play style to game advice, from environments to equipment. Advanced Dungeons & Dragons was supported by a monthly game magazine called Dragon, with optional rules, advice, and ideas. The Castle Keeper's Guide contains several years worth of quality Dragon items in one hardcover. It truly enhances the game, while not being strictly required for play.

I read the PDF of the third printing, recently on kickstarter, though I did not go back and compare with my earlier print edition. The artwork here is really nice, evocative of situations and adventures. The alternate cover joins in story with the 8th printing of the Player's Handbook, also recently on kickstarter. I read the book cover-to-cover, which I hadn't done with my print edition. While I wasn't reading with a proofreader's eye, I found only one misspelling on page 310, part of the "Ebb and Flow of Battle" section - and that looks like a paste error. A very good record for a 372 page book.

Overall, if you are interested in an "old school rules", I recommend Castles & Crusades in general - and this book in specific and an excellent reference for game play, optional rules, situations and ideas.