I took this course (part 1 of 3) last year and passed it with about 90%.
It left me with a question in the back of my mind about whether this is a very watered down version of the actual Harvard course (I hope it isn't) or if they're just that good at teaching it. Because there is never a stumbling in understanding something, the course just flows naturally from one lecture to another and you get immersed into it all the way through.
If I recall correctly I saw all the lectures during 1 or 2 evenings and did the final exam a week or so later and surprisingly the material was retained in my head.
I wish they wouldn't say that it's free. It's not free if you have to hand over a bunch of your information in order to see the content.