Sometimes classes on things you already have a strong foundation in can be like that I've found. You get bored to sleep for the first chunk and by the time they catch up with what you know you're on your back feet trying to figure out how they're talking about things. That, or the busywork is just infuriating (I run into this occasionally on Coursera).

I've always generally done much better with self directed things, though I do like discussion as a way to ensure I know what I think I know.