From the Introduction:
Overlook is a game in which you and 2-3 of your friends will construct a fantasy world by following the journey of a group of explorers and adventurers as they travel though that world. You'll describe sinister city streets, ancient temples overgrown with horrific death vines, and the Prison of Demons hiding just below the surface of an idyllic lake. You'll generate factions and communities to fill that world, striving for both good and evil. By the end, you'll tell the story of your explorer's discoveries, and her triumph or failure - and you'll be left with a dynamic world full of adventure possibilities. Overlook can thus be used to generate a setting that your group will explore with another game. But it can also be played as a self-contained game for an evening's entertainment. The game should take about 45 minutes per player.
Overlook is a role-playing game in the sense that you will invent characters to inhabit as you play the game, characters you should care about and cheer for. But it is also a story-telling game in the sense that you will often step away from those characters to author details of the world – many of which will conflict with your character's goals. It is not always easy to move between these viewpoints, but keep the dichotomy in mind as you play.