Professor Denef is very nice and will answer whatever questions you have. He's very responsive to emails and sends detailed replies to homework questions. However, don't expect to learn anything from the lectures. The homeworks typically have nothing to do with anything Denef talks (or rather, mumbles about) in class, and you will be teaching yourself the vast majority of the material from the textbook. When the homework is easy this isn't a problem but as the class gets more and more conceptual and the mental leaps you have to make are greater, this becomes very frustrating. He does say very funny things in class sometimes, even though I learned more about thermodynamics studying for the GRE than I did in this class.