Professor Gekelman is a nice person and a fair lecturer. If you pay attention in class, there is no way you will not get an A for his class. A very fair grader with optional homework (this helps people like me a lot), he curves generously. Overall, a pretty good professor. On a scale of whether I'll recommend him to a friend, definitely!
Professor Gekelman is a researcher, not a teacher. His method of approaching physics is the result of a life of calculations and complex simulations. He thinks on a whole different level than undergraduate students, believing that things like exponential functions dealing with imaginary numbers should immediately come to us after a normal high school education. He does not seem to understand that he has spent his whole life studying physics, whereas the majority of students taking his waves and electromagnetism class have only had roughly two years of experience. This gap between the professor's and student's knowledge base and the disregard of this gap by the teacher highly detracts from the learning experience of us students. On the other hand, Professor Gekelman is a very friendly man. He does care about his students, even if he doesn't know how to teach them. You could almost call him the nice grandfather type (btw the bruinwalk picture of him is waaay old). I'm sure if you go to his office hours he will definitely be willing to help you to understand the material from the textbook and his supplemental equations for the textbook. To sum it all up: Walter Gekelman does not know how to teach undergraduate students, but he will definitely be willing to help you if you go to his office hours. Other things: He has weekly quizzes, his Physics 1B class is curved, the midterms occasionally deal with his "supplementary" material, he teaches through slides, and he sometimes tries to derive equations on the blackboard (with lots of mistakes).
Winter 2019 - Plasma physics is a really exciting field because of all the advanced technologies that utilize it. Gekelman has been a huge figure in the field for decades so taking this class with him is really a cool experience. He makes some algebra mistakes sometimes, and the slides can get pretty dense with the mathematics, but Gekelman always makes sure to teach the physics of it (it can be easy to get bogged down in the math if you try to write it all down, focus on what he is saying instead). Make sure youre E&M is strong, and maybe brush up on some basic fluid dynamics, because you really hit the ground running with this class. Overall, a really great class, one of the more difficult classes I've taken out of the physics department.