From the website: "Design Patterns of Successful Role-Playing Games contains patterns gleaned from a study of many traditional and cutting-edge role-playing games. Game Summaries of the source materials are also included."
From the introduction: "RPG design patterns are not about deciding upon a creative agenda, genre, or even helping you clarify your design goals. RPG design patterns are about formalizing the mechanics observed in existing pen-and-paper role-playing games, the kind of games where the players sit around a table and actually talk to one another. Each pattern description discusses its particular strengths and weaknesses, and educates game designers interested in using the same techniques on how to properly implement them.
This study focuses exclusively on the nitty-gritty structure and mechanical design of table-top role-playing systems. RPG design patterns have nothing to do with mood or setting, although these issues are obviously quite important to many games. In other words, design patterns approach game development at a micro level rather than a macro level. For example, if you have decided that you want to abandon hit points as a means to measure character survivability in your fledgling game, what are your other options? What about alignment? Are there better ways to guide character behavior? Are character classes the best option for your design goals? If so, what pitfalls should you avoid in implementing them? If not, what are the alternatives? How should conflicts be resolved? Is there more than one approach? "