Web-based resources and massive open online courses (MOOCs) are promising forms of non-formal and technology-enhanced learning. Advantages are the flexibility regarding location and time and the possibilities for self-regulated learning. Furthermore, web technologies have considerably evolved over the past years, enabling complex interactive exercises and communication among the learners. However, online learning also has its challenges regarding, e.g., the motivation and low-completion rates in MOOCs. Following a design-based research methodology, we designed, developed, and evaluated a MOOC for the introduction of object-oriented programming. In three course runs, we collected extensive textual feedback from the participants which we analyzed inductive qualitative content analysis (QCA) by Mayring. We complement this with quantitative analyses regarding the performance of the learners in the course. The results give insights into the progress, preferences, and problems of learners in MOOCs. We furthermore used these results as a basis for adapting the course in the following iterations of our design-based research and observed a significant increase in the course completion rate.