The quality of a course really depends on who is running it and how enthusiastic they are. So I would recommend keeping an open mind about coursera until you've taken a few different courses.

Also depends on the students that take it. Sometimes you get incredibly helpful people taking the course - that seem to know everything and beyond - and don't mind taking the time giving really detailed explanations on the forums.

I'm doing the calculus course atm - and enjoying it a lot.