Over the past few months I have completed three courses on Coursera and audited a couple of others. Now I've just signed up for another two, one of which I will complete and the other of which I will probably just audit. Overall, my experience has been a positive one. I'd like to set down my thoughts.
There is a lot of variation on quality between courses, as well as a lot of differences in the levels of prior knowledge expected of the learner. The amount of work that is required also varies a lot and doesn't always correlate with the stated expectations when you sign-up. This probably explains why I didn't complete a couple of courses. I simply got behind and so can only claim to have audited them (i.e. dipped in)
The quality of the lecturers I have encountered so far has varied from poor to excellent, but by and large they have been OK. The degree of preparation of materials and syllabuses has also varied a lot between courses, but again it has been mostly on the good side of satisfactory. More than you have any right to expect from free offerings.
I have chosen subjects in which I am not already qualified. These have been exclusively from the arts and humanities, since my formal qualifications are in science. In general, I find I have had to supplement the online material (videos and texts) with books that I have borrowed or bought. This may be because of the way I have previously learned to study.
My objective in taking these courses has been to learn useful stuff and, in my opinion, this objective has been achieved beyond what I had expected.
Although I am not personally concerned with gaining a formal qualification, in the three courses I have completed so far I have done all the required assessments and participated in the peer review. Assessment generally consist of multiple choice quizzes and essays or projects that are marked by other students on the course.
This peer review of work is a concern, moreso perhaps for those hoping to gain a qualification, since the quality of the reviewer weighs heavily in the mark you get. That said, my personal experience is that reviewers often mark high, perhaps out of self-doubt. Sometimes you get an arrogant or angry assessment from someone who (giving them the benefit of the doubt) knows their stuff and thinks your work is below acceptable standard. This can be a bit discouraging, but the fact that you get an average of all your markers means that statistically this doesn't usually hurt you. Unfortunately, the generosity of the average marker probably means that poor work still gets good marks.
One way in which I was not a typical student is that I was reluctant to engage too socially in the course and so didn't get involved in the discussion forums, although I did read them and very useful they were.
In all my courses, including the ones I only audited and the ones I am following now, I learned a lot of really useful stuff.
MOOCs of this sort are an excellent source of material for all sorts of people, including full-time students who should monitor those from top Universities as an additional resource to the resources provided by their own colleges. Indeed, colleges ought (if they don't already) to be evaluating the available MOOCs and recommending them to their students.
MOOCs are an excellent addition to traditional learning from books (for most of us) and from lectures (for those lucky enough to be at college). Who knows, in future they may become the primary source of advanced education for most of us. They certainly have that potential in the hands of the right teachers.