Williams is pretty good. He speaks in a monotone, so if it's an early morning class, you'll have to get some coffee.
I will say that MATH61 is brutal over the summer session, though. There's a tremendous amount of information crammed into 6 weeks and little time with which to practice exercises in between lectures.

Like I said, WIlliams is a good guy, but summer session is not the optimum time to take this class, IMO.

I took his 32A and 61. Professor Williams is a good teacher.

He looks quiet but in fact his is approachable and cares much about his students. Usually, has two midterms(one in summer) and quizzes and allow you to drop the lower midterm. The quiz is easy and always the exact same question in his homework. I like his exam questions because they need you to take a while think for a while but never unsolvable. In order to have a decent grade in his course, you need work hard and I nearly did every questions in the book no matter he made it homework or not. The questions in his exam are similar to the questions in the book but not exactly the same.

So, my experience is do as many questions as possible and you should be confidence of yourself. And that is the key to be successful in math isn't it?