Bryan Loyall cites expertly paced penguins in this response to Janet Murray.
Another criterion we have found important for interactive dramas is that they have compressed intensity. It is important that the story move at a reasonable pace and never get stuck. This is at odds with many games based on solving puzzles. If the participant can get stuck, then the story doesn't progress, and the compressed intensity that is a hallmark of many traditional stories suffers.
Compressed intensity can be achieved by sharing the advancement of the story between the participant and the world. In a prototype interactive drama system, The Penguin Who Wouldn't Swim (1999), the participant is a penguin who is trapped on a chunk of ice with two other penguins, drifting out to a dangerous sea:
Fig. 1-5.: The Penguin Who Wouldn't Swim. (Zoesis)
One of the penguins wants to stay, and the other wants to try to swim back to shore. The participant is always free to do as she wishes in the situation. To adjust the pacing, there is a dramatic guidance system that continuously estimates the participant's subjective feeling of pacing. If that pacing is good, the system does nothing, leaving space for the participant's actions. When the subjective pacing is bad, the system acts to advance or slow down the story as appropriate, using the characters and other active elements. (As this is going on, the dramatic guidance system is also acting to guide the flow of events toward the author's story.)
All of these criteria are related to those of traditional stories and games, yet many are different in important ways needed for interactive drama. Murray urges us to not be limited by the dichotomy between stories and games, but rather to recombine and reinvent their primitive elements. In working to build these systems we have found that this is not just useful, but necessary. Interactive drama allows us to tell stories that we couldn't tell before. It combines strengths and elements of stories and games, and is both and yet neither. If we are to reach the potential of expression that it offers, we must work directly in the new medium to explore, experiment and build.