The study examines massive open online course (MOOC) students' engagement and learning challenges while comparing two groups: xMOOC, a structured course based on individual learning, and cMOOC, an interactive course based on collaborative learning. Applying a mixed-methods research design, data were collected via an online survey and semi-structured interviews. The findings indicated differences in students' "engagement profile" between the two groups. The xMOOC students asserted high means for cognitive and behavioral engagement, whereas the cMOOC students asserted high means for cognitive and social engagement. The main challenge for xMOOC students was the complexity of course content, while the cMOOC students were more concerned about technical problems. The results reinforce the need for teaching staff to adjust student support according to MOOC type.