obSESSION is more than just a Role Playing Game, it is a set of core mechanics designed for use with any setting, genre or game style. The fully expandable rules contained in this book are adjustable for a variety of playing styles and can be used to model any reality that the GM or designer can imagine.
Additional optional rules from Obsessive Compulsive Design are fully compatible with the rules found within, expanding upon rather than contradicting the core rules and ensuring that any optional expansion is usable with any obSESSION game, not just one or two.
GMs and designers can choose the level of realism they desire and balance it against a number of player-friendly options to create the game and experience that they want. By building from a consistent base model of reality obSESSION allows for the rules or settings to be “tweaked” without losing compatibility. It’s internal consistency also allows for a minimum of mechanics to cover a maximum array of potential situations and makes “on-the-fly” rules decisions simple.
The Core Rulebook contains enough to begin play usig the obSESSION system. Character creation, game rules and the beginnings of the framwework with which obSESSION allows you to model any genre, style or setting are all found within. A complete campaign can be written with a little work from the GM but these rules are expanded upon and complemented by the material published separately in the Appendices and many more advanced topics can be found in those files. Prospective obSESSION GMs who are interested in such advanced topics are advised to check the Beta Edition of the Core Set, which includes access to the ongoing development of the Appendices, but this document is all you need to start playing, especially if combined with one of more of the Capsule Settings available from OCD.