Understanding the interactive experience of using digital technologies is a complex process. Traditional methods of evaluating interactive technologies originate from usability, which focuses on ease of use, ease of learning and performance. User Experience (UX) emerged from the recognition that usability alone does not account for the more subjective emotional responses experienced when interacting with a product. Although the term UX has become widely accepted within the area of Human Computer Interaction (HCI), its definition still remains unclear, making it difficult to evaluate and design for. This thesis adopts a hybrid perspective by bridging the division between the reductionist and holistic approaches to UX research. Using a multi-methods approach that combine the strengths of both quantitative (objective) and qualitative (subjective) methods, will provide deeper insights into the users' judgement process of interactive products. Various theories have been proposed to understand UX, yet no consensual UX theory or model has emerged. The importance of aesthetics in influencing decisions about a products quality gained much attention in early UX research with conflicting results, sparking a surge of research into understanding the complexities of user quality judgement. Past UX research has focused on the multi-constructs of pragmatics, hedonics and aesthetics, and how these may influence user judgement, which can vary depending on the context, task and user background. However, little attention has been given to the impact of interactive design features upon UX. Findings from this thesis clearly show that interactivity is an important element within UX in both short and long-term usage. This thesis expands the existing process model of user quality judgement, through a series of three studies to reveal the importance of interactivity, and how initial perception and judgement of a products quality can change over time. The first two studies identify the importance of interactivity in positive influencing UX. Both studies revealed that affective and hedonic ratings increased as a result of interaction, demonstrating the powerful effect of interaction, and showed clear differences for websites that contained enhanced interactive features, despite the presence of usability problems. Further exploration using cluster analysis revealed three sub-groups that categorised users not only by their interactive style preferences, but also by their predispositions towards technology. This perspective of user sub-group analysis is a contribution to the field which bridges population-level quantitative analysis with qualitative findings that focuses on the individual ethnographic interpretations of experience. Considerable UX research has focused on short-term evaluations, based on users first impressions pre and post-interaction, with few studies capturing long-term usage. The third study reports on an ecological longitudinal investigation into how UX changes over time and long-term product use. A group of novice iPad users were tracked over six months to reveal that despite poor usability, hedonic ratings remained high, yet over time usefulness and utility were dominating factors affecting UX and product adoption. The influence of both device and app revealed that although users found the device more pleasurable, it was the variety of apps contained on the device that facilitated positive UX. The overall findings from this research provided some valuable methodological insights and aided the creation of set of practical UX heuristics that can be used to inform both future research and design practice.