Not too easy. Not too difficult.
The class itself isn't difficult; professor Zhang is just very soft spoken and what you learn in class probably won't be on the exam. If he shows you something really difficult or confusing, I would recommend writing it down and getting additional help on it because it will most likely be on the midterms and final.
The class was curved pretty heavily and the TAs were really helpful. A lot of the class is covered if you had taken Calculus AB in high school so there's more time to go into depth and secure your understanding of the harder material.
Hours per week:
Advice for students:
Don't procrastinate and wait to the homework. There is always more than you think. Pace the assignments and it's not too bad. Also form study groups. There's always groups that you can find that also need the help and want to practice difficult problems.