I second this! I have taken 7 Coursera classes, and most of them "lightly": just doing as much work as I needed to for passing the class, with just a few classes that I did put a lot of energy into. Andrew's class was in this second category: I kept taking the tests and tweaking the homework assignments over and over again until I got a 99.5% score in the class. His class was lots of fun and also very useful material. Recommended!!