I started my journey with MOOCs through the edX platform last year. It was nice getting back into a structured way of studying again, so I completed (with distinction) 6.00.1x and 6.00.2x (with a verified certificate!) from MIT’s Computer Science track. I then completed an R course before realising that edX makes you a do a lot of work. Just, a large amount of work, especially if you are working full time and learning extra for your job in your own time. I checked out Udemy as well, but haven’t looked at it again now after completing the first ESRI MOOC last week. I wasn’t too enthusiastic about the interface Udemy uses.
Coursera, on the other hand, is great. When it works. A nice selection of courses (I’m doing 5 at the moment!), with reasonable workloads. I’ve taken courses which will hopefully support my Honours studies for next year, such as Stanford’s Introduction to Logic. The course has been quite intense so far, but the notes are very good.