I agree that he can be incredibly cranky. He really dislikes questions that are thinly veiled attempts to determine the content of the exam. He is not fond of academic prima donnas who expect an A and aren't afraid to let him know it. My impression is that he has little patience for interactions that indicate more concern for the letter grade than for learning the material. Avoid these transgressions and you should do OK with him. Do NOT take his crabbiness personally.

Having said all that, I thought he was one of the best professors I've had at UCLA. His lectures were excellent and made a difficult topic very clear. He was by no means "easy", but he gave us all of the tools we needed to learn the material. He answered questions posted to the webpage promptly and thoroughly. Exam questions were sometimes difficult, but straightforward. Hard work in this class really pays off.