He was definitely one of my favorite professors. He's really fair about his grading, and he gives a really generous curve. I thought he was really funny during some of the lectures, but that may have just been me. He gives plenty of examples during his lectures, so the homework and the exams are pretty straight forward with maybe one more added element. I felt the exams were really easy, and anyone who has legitimately taken any physics class prior to this would be just fine.
This is quite possibly the worst professor at UCLA. To start, the book he chose to teach the course was full of errors, many of which he noted himself. His lectures were just filled with formulas and derivations which he failed to explain, and his notation was inconsistent, making it difficult to follow. He was unhelpful during office hours and sometimes could not even answer the questions he assigned. His TA was extremely lazy and was never available. Don't take a class with Williams, it will ruin your quarter.