This dissertation presents a multi-method approach to study the user experience of playing video games. The motivation is to devise an objective assessment of the concept of user experience. It is proposed that user experience is better understood when it is studied as a two fold phenomenon formed by a process and an outcome. This definition allows combining the subjective nature of experience together with the objectivity needed to propose an objective assessment of experience. An experience is personal in the achieved outcome, during the process of forming it there are elements specific to the type of experience common to all individuals. The contributions of this dissertation are: a novel approach to understand user experience as a falsifiable concept, a theory and metaphor to describe the gaming experience, a model that describes the gaming experience, and an instrument that can be used to assess and explore different gaming experiences.