The course, somewhat ironically, was "Fundamentals of Online Education: Planning and Application" (the description was still online this morning) and an article on insidehighered.com explains some of the problems with the course. It looks like it was a combination of technology and design issues.
The instructor, Fatimah Wirth, emailed participants and said: "We want all students to have the highest quality learning experience. For this reason, we are temporarily suspending the 'Fundamentals of Online Education: Planning and Application' course in order to make improvements. We apologize for any inconvenience that this may cause. We will inform you when the course will be reoffered."
Although students were not paying for the course, they were still angry. The facts that it was a course about online education and that it was offered by Georgia Institute of Technology just made the crash seem worse.
One tech issue was that it was intending to use Google Docs to sign up for group discussions and that application couldn't handle the demands of 41,000 students. (Google spreadsheets limit you to 50 simultaneous editors.)
It also seems that the demographics of the participants was quite "professional" with college and K-12 teachers and people working in online education. So, expectations were high.
Although there is no information from Coursera, the instructor or GIT on what actually went wrong, the article points out that students posted on social networks and blogs about their experience. (One review is called "How NOT to Design a MOOC: The Disaster at Coursera and How to Fix It.")
I am not shocked that a MOOC failed. I feel bad for the students, but I also feel bad for the providers. I would not want to be the first MOOC to get widespread media coverage for problems. I am sure other MOOCs have had similar problems and that some have shut down - but this one is getting the spotlight.
The real importance in this instance is to look at what went wrong and use it as a way to better design courses online. There are lessons here for "massive" online courses, but also for the more typically smaller online courses that almost every college is offering.