After last year’s excellent Rules of play (Salen & Zimmerman 2004) now everybody recommends:

KOSTER, RAPH. 2005. A theory of fun for game design. Scottsdale, Arizona: Paraglyph Press.

For background information see the according entry at game matters with extensive comments, and Conversation with Raph Koster by Celia Pearce. And if we’re talking about ‘definitive’ books on computergames, here’s a hint: Chris Crawford’s classic The art of computer game design is online already since 1997. Just to round it up, the ludologist points to The evolution of gaming: computers, consoles, and arcade, another take on game history. And then, academics concerned with games, get always_black and its repository of non-fiction articles, the black_box on your radar, just as Rex has proposed—tnx for that. Not that I am an evolutionist, stating that graphic novels are the evolutionary predecessor to computergames, but of course there are connections between those ‘genres’. Hence another classic:

MCCLOUD, SCOTT. 1993. Understanding comics: the invisible art. Northampton, MA: Tundra Publications.