i think after the horrible tests in winter 2021, he toned them down. granted they were still hard but it was mostly doable.

Avoid at all costs. Makes 20B harder than it should be.

I think Barr is passionate, but my experience with him was terrible. The exams were tough, and he would not listen to class feedback. To be honest winter quarter was just a nightmare all over. The whole class experience was akin to experiencing a firebombing 24/7. That said, I understand it was his first time. I just wouldn't take him again. UCLA Chem department needs to do better, as their restrictions during covid probably was also terrible and made it harder for Barr to accommodate us. I heard he got better, so take my review as you will. I just can't say he was a good professor based upon my experience.

For it being his first time teaching, Barr was decent. He's very enthusiastic, passionate, and invested in our learning which is nice having a professor that cares. Also, he provides a lot of resources for practicing the material and provides students with opportunities to get help in terms of office hours, campuswire, review sessions, and being open to questions during lectures. He's quite helpful when you ask him questions directly through audio and patiently and thoroughly explains the concept until you understand it to your satisfaction.
A lot of the negativity towards him comes from his insanely difficult midterms, which is fair as they are very difficult. However, his final, which was still challenging, was significantly easier than the midterms and has a much greater affect on your overall grade, giving you a chance to improve you grade significantly even if you did poorly on both midterms. Nevertheless, you do need to put in a lot of work for the class, as there is a lot of material to learn, understand, and master. It is quite a difficult course which can be a little disheartening at times but you definitely learn a LOT and in the end it works out better than expected.