"experiential density" — the amount of "things" that happen to and are done by the player per unit of time and area of a map. Our goal was that, once active, the player never had to wait too long before the next stimulus, be it monster, special effect, plot point, action sequence, and so on. player acknowledgment. This means that the game world must acknowledge players every time they perform an action. For example, if they shoot their gun, the world needs to acknowledge it with something more permanent than just a sound — there should be some visual evidence that they’ve just fired their gun. We would have liked to put a hole through the wall, but for technical and game flow reasons we really couldn’t do it. Instead we decided on "decals" — bullet nicks and explosion marks on all the surfaces, which serve as permanent records of the action. the players should always blame themselves for failure. If the game kills them off with no warning, then players blame the game and start to dis