[leggomylibro]

Hands-on, practical examples. If a class only includes video explanations and some quizzes on what was said in the lectures, I usually forget the subject matter quickly. The best MOOCs that I've taken are the ones that have periodic "lab" assignments which ask me to think and apply the subject matter in ways that the lectures may not have explained in precise detail.

Without naming names, here are two examples:

I once took a MOOC about "bare-metal" microcontroller programming which didn't include any microcontroller coding. Useless.

I once took a MOOC about digital circuit design which used an in-browser circuit simulator for problem sets and labs. Extremely helpful.

I feel sort of cheated when I work through an online course, only to find out that it would have worked just as well if it were a series of YouTube videos.

For college-level data structures, maybe you could ask students to implement their favorite DS from a set of tricky ones? You could write automated tests to verify them so grading is easier for you and development is easier for them.