If you are looking for ideas for a game, this is the book for you. Looking for advice, this is the book for you. Trying to find one of the many optional rules of GURPS, this is the book for your. Trying to find some obscure advantage or skill, sorry but that is Compendium I. This is the book for the Game Masters out thier. It is full of detailed rules from everything from poisonous gas to characters getting drunk (a necessity when the party includes dwarves). I would consider it a core book for the game, not necessary to play but very useful.