In this article, we define interactive storytelling as a gaming experience where the form and content of the game is customized in real time and tailored to the preferences and needs of the player to maximixe enjoyment. The primary focus of interactive storytelling should not be on the attributes of the technology or characteristics of the medium, such as the AI techniques, planning formalisms, story representations, etc. but on different interaction levels provided by computer games and basic components of player enjoyment such as difficulty levels and gaming rewards. In conducting an analysis of interactive storytelling systems, we propose a user-centered approach to interactive storytelling by defining different customization levels for an optimum gaming experience.