Good

Prof. Duan is a very friendly and nice guy. But, this class is really hard. I'd advise you not to take this class with him if geology isn't your thing. He offers extra credit and makes well-organized powerpoints. The material is in-depth and there are actually tons of material which can get really overwhelming. He isn't a bad guy though. It was just a really hard class.

Poor

Prof. Duan's tests are very detailed. For a non-major class, he also goes into minute details. He's a really nice guy but I don't recommend taking him unless you are willing to study every day. He doesn't have a clear grading criteria, but he offered extra credit. He required only two exams and a cumulative final that's pretty detailed. If you aren't majoring in geology, I wouldn't recommend taking him.