I've completed a bunch of Coursera courses. Quality really varies. Even within the 9 course Data Science specialization [1] track some courses were rather poor while the rest were very good. I'm currently taking the #5 rated course [2]. It is excellent. But I'm only taking it because the Statisical Inference course in the Data Science specialization was so weak.

I would also recommend the Cryptography 1 course by Dan Boneh on Coursera [3]. Excellent if you are at all interested in the subject.

I always download the lecture videos, slides, quizzes, labs and exams because, as mentioned, many of the courses don't allow access once the class is completed.

You definitely have to have plenty of self discipline to complete MOOCs. And I don't have any delusions about a Coursera certificate being useful in landing a job; that's not what I'm after. I'm building the skills I want to apply to my own projects.

[1] https://www.coursera.org/specializations/jhudatascience [2] https://www.coursera.org/course/statistics [3] https://www.coursera.org/course/crypto