Kristina Šekrst completed this course and found the course difficulty to be medium.
I'm a huge fan of Uni of Alberta courses, since they are always so cleverly designed, along with great videos and course materials. This was no exception. It's a new course, but it deals with the currently hottest topic since the picture of a black hole. You'll learn the basics, and slowly go over more complicated maths and physics, but I believe everybody with high school mathematics should be able to follow most of it, there is no calculus so far, or difficult calculations. But theoretical concepts are advanced, even though they are lectured clearly and concisely, with nice expert interviews as well. It's a big course, but worth your while.