Brilliant at physics, but you can't tell by his thick accent. Also, the problem with his class was that he taught the material as if you already knew it, not as if you were learning it for the first time. This was the big issue for a lot of the people in the class. But his tests weren't that bad, and he's a very generous grader. If you're competent in physics, take this class. If it's all new to you, I say you should try to take a different professor.
I had him for Physics 105A and 105B. It seems like some people don't like him because of his thick accent, but it is pretty understandable and if you are ahead of your reading you will find his lectures are pretty good. His tests are open book and easy. His grading method is generous. When I visited him during his office hours, he seemed to be very concerned.
Professor Pellegrini is not a bad lecturer. Yeah, he has an accent, but it never bothered me. His tests were not bad at all, and very generously graded. When the class did poorly on the midterm, he actually scheduled another one so that we would not all have terrible grades. More relevant homework, meaning homework that was not straight from the textbook and instead closely tied in to what we actually learned in class would really have helped. Okay lecturer, generous grader, and just generally laid back about everything. Good for a senior who is anxiously awaiting graduation.