Barr's class was the worst class, no the worst experience of my time here at UCLA. The material that this class covers could and should constitute a fairly relaxing class. None of it is overly complicated or difficult in and of itself.
However, Barr somehow manages to make this likely one of the worst classes across every UC. The false confidence that you are given from the extremely simplified and surface level lectures is instantly annihilated by the slaughterhouse that is the first midterm. IF you manage to escape and survive the darkness of this valley, there is no true peak to be found. Just as you start climbing the other side, the floor falls out below you and you plummet into a pit of pure torture, the second midterm. No matter how much you prepare for a midterm with the same difficulty as midterm 1, you will not escape this impending doom. (The average of this midterm was in the low 60s and was not curved).
While this pattern could also somewhat be found in Shao's Chem 20A class, the final provided an oasis at the end of the quarter. Barr did not. The final was the worst test by far. Barr said himself, and I quote, "This one is a doozy." Now, if you are still considering taking this class, note that it is not just the tests which are bad.
To save time I will list the rest of my complaints in bullet point fashion.

-No answers to any practice problems unless you go to every "optional" office hours
-Not even TAs were given all of the solutions
-Office hours by Barr were far too slow and rarely got to difficult concepts
-Some people had to retake this class for scoring too low on the final even though their overall grades were high C's to low B's (would not budge on bumping people 1% up to the bar(pun intended))
-Group homework assigned Friday night and due early Monday morning
-Assignments on about 50 different websites which are very easy to miss
-Somehow make you feel like its all your fault

Don't take this class. I know you have to. But don't. Take it at a community college if you have to.
Only advice I have if you are unfortunate enough to take this class:

-realize GPA isn't that big of a deal
-go to TA office hours

Im sorry

Like many others, I was allured by the veneer of understanding Dr. Barr has. The initial emphasis on mental health and wellbeing was supportive all well and good until tested. His empathy seems to extend quite far in his speech until the actual exam. Besides the convoluted absurdities asked on the exam, and his unwillingness to scale, even in a global pandemic when people are taking the class online in every time zone, for freshman general chemistry! That's not very empathetic. I cannot imagine a general chemistry class being unscaled at a university like UCLA. However, I wanted to give him another chance for the second exam because I was thinking he would listen to student feedback, but as I suspected, absolutely no changes were made in the manner in which the questions were asked. Much of the lectures are filled with superfluous, unnecessary speech which makes chemistry (an already difficult enough subject) all the more complicated. The "systems" of the class are overly complicated and unnecessary. There are two portals for surveys, homework assignments are collaborative without any decision made by the student. It is clear that we are the first round in a new-age type pedagogy and it's not working. The only good thing about this class is the GroupMe, where it is a community of 500 students all bonding over the constant suffering of this class, and collective outrage at many aspects of this course. Do not take this class!!

No matter how much you study, it won't be enough. The midterms are very difficult and all application questions with probably more biology concepts than chemistry. On top of this, Barr is extremely stubborn and does not even take into account the surveys he makes us do. I just do not understand how this is allowed, ESPECIALLY BECAUSE THERE IS NO CURVE! He claims that he is "empathetic" to us because we are in troubling times, but then he troubles the troubling times by giving us exam questions we know nothing about.

Pros:1. The professor seems like a nice person

Cons: 1. The tests are little related to review sessions, homework, and lectures
2. No curve
3. No extra point
4. Feel like chemistry is so scary
5. Really frustrating feeling when taking this class

Advices for people want to take this class: don't put so much time on review sessions because then you would find out that you are "studying for a different exam".

The chem department as a whole just does not care for its students and Professor Barr is just a product of that. He tells us that he can't give 24 hour exams because "his hands are tied" and "it's what the department has mandated". This would be fine if this was true because then he truly couldn't do anything. However, this is all a lie. The Chem Labs give 24 hour exams and I heard that the Chem 20BH get 24 hour exams. He also told us that the first midterm would be easier than the homework. Again another lie. Lying to his students is just one of the many things that I don't like about this class. The other thing I do not like about the class is that in our discussions, the TA's and the LA's try to be as helpful as they can be but what is the point if you aren't going to test us on the things we've been studying. Professor Barr also likes to say that he "empathizes" with our situation. He can say it as many times as he wants but if he does nothing to address the many issues that we students come to him for, then he might as well say nothing at all. He does not accommodate for international students either. Even when you spend the extra time to go to his Office Hours, he barely helps you and instead gives you an answer that just leaves you with more questions. Again Professor Barr is just a product of the Chemistry Department not caring. After someone in the class sent an email to the department begging to understand the reason for all of this, the department implied that Barr is a great professor and very qualified. Ahem I don't know if being very smart makes you qualified to teach but I guess I wouldn't know since I'm a student. But I guess the department wouldn't know either since they can sit at the top and act so aloof. You can't ask a principal to understand the struggles in a classroom because they never sit in there day in day out so how would you expect the "prestigious" Chemistry Department of UCLA to understand the struggles of a student in a global pandemic mind you. I hope that Professor Barr does at least try to learn from all this because there is hope, but the way he is right now... avoid him.

WORST CLASS EVAAAAAAA!!! There was more focus on encouragement than teaching chemistry. He wasn't tolerant and didn't care about anyone's personal issues, such as getting covid. He made it way more difficult to learn than it had to be by never giving answers and sometimes gatekeeping information in his lectures. The class was always treated like elementary students. He actively tried to hide answers and "encourage collaboration" where it wasn't helpful. He used multiple different websites and apps throughout the course making it difficult to keep up with the work. Barr would barely answer specific questions on material and proceed to put that same material on exams. He makes the most complicated test questions about random real life products/events which are difficult to answer with the little teaching he gives on those certain topics. His borderline creepy obsession with Disney has also ruined any good experiences I ever had or will have with that company. I never want to take a chemistry class again and especially not with a teacher that talks about helping his students so much when he is actually inhibiting our learning with the ways he hides information and answers from us. I never want to see anything related to buffers, acids, or bases again out of fear for the PTSD it will bring from this horrendous class. This man's purpose of making the class more difficult than it should be seems to be overshadowing his passion of teaching and ruins any chances of easily learning. His tests progressively got harder while switching from online to in-person which became really difficult with less notes allowed in person and more challenging material. Never taking a class from him again and god forbid anyone else has to either. FUCKIN WEIRDOOOOO!

The group you get in is probably the most important thing. I tried to change my group at the start of the quarter but thanks to the TA that did not happen. Then, I had to do all 4 homework by myself for the whole quarter. Barr's a nice dude but you'll hate him for the way he designs his 20B class.

My opinion on Barr pretty much aligns with everyone else's. I honestly think that he's a nice guy who cares about teaching, which automatically makes him better than a lot of other professors, but he's just so new and it takes time to iron out a teaching and test writing style that works. There is a lot of mandatory group work, and I got very lucky with an excellent group so that ended up helping me a lot, but it's all up to chance and I understand how people could be mad about that. I actually felt that the workload of the course was pretty light, with only 4 homework assignments due in the quarter graded by accuracy and weekly pre-lecture activities that hold your hand the whole way through. The two midterms felt like the extra challenge problems at the back of a textbook that no one likes, just too detached from the material to feel fair. I felt like the final was a very big improvement over the midterms (probably due to people complaining in his emails) with much more straightforward questions, and if you scored better on the final than one of your midterms then he counted your final score twice instead of that midterm, which was cool. I feel like all of these negative reviews will be kinda pointless in like a year as I think he will improve very much, but if there are other professor options with good reviews then I can't recommend Professor Barr over them in good conscience.

Straight to the conclusion, Barr deserves a much better score than 2.3, at least in the Spring quarter. I gave him a 5 (more like a 4.5)
From my experience in the spring, I would recommend him. His lectures are not bad, for him being a funny and engaging lecturer, though he sometimes goes off topic....; He gives a LOT of assignments(many of which are VERY EASY TO MISS, BE CAREFUL), so the workload of this class is heavy, though the good part is that they boost up your grades for them being easy 100s; The tests are difficult for sure, (cuz it's chemistry), but they are on topic and relatable to the class content (a GREAT improvement from winter as I looked at the past tests). Grading is fairly generous and based on a curve. (Class avg for tests in my session are like mid-70s, so an 80+ would probably give you an A unless there are too many prodigies alongside); Group participation does matter, good thing is that this time he lets us pick our own team. And I appreciate him for this because my teammates and LA are GODSEND!! what I dislike about him is that grading for him takes forever, expect more than 3 weeks for each test.....
A big problem about him is that he gave us problem sets as test review materials (not part of the huge workload), but there are no answers (which make the problem set meaningless), you are completely on your own and the only way for help is OH/review sessions which is not enough. luckily my GODSEND LA gave me his solutions and helped me review, so I didn't suffer so much.
20B in general is not as hard as 20A, most of the contents are reviews/expansions from AP Chem topics. If you did well in AP then you should ace this easily, if you didn't then don't worry, there won't be any quantum mechanic shits like that in 20A.
I had friends who took him in winter and I understand all the earlier negative comments about him. There still are many parts of him and his class that I find it struggling, but he actually listens to students' complains and suggestions I have seen those improvements made in spring. Since he is a new prof. so be easy on him, plus he is a very approachable and friendly teacher. For future students, if you find it struggling in his class, write something serious and helpful in Bruinwalk or direct email so he can improve and teach better.

I told myself that I would wait until I was done with the class to really make sure that what I was saying reflected the class as a whole.

As you've heard, this class, for all intents and purposes, sucks. Do not take it if you have the opportunity. My caveat to most of the other reviews is that this not only was Barr's first year teaching, but he also was given the entire 20B course to handle on his own. I don't think he's the devil in Disney's clothing. I'm pretty sure his ideologies and test styles would have been a little more fruitful if he didn't have the entire 600 student load to work with.

On the other hand, there is a lot of things wrong with the class. The emphasis on group work, especially given the times that we are in now, was a miss. The lying to the students was disappointing. The tests that didn't really mirror content in the class were painful and disheartening. But the worst to me, and many others, was the refusal to listen to our complaints. I understand that he had research on how students work, but there comes a point where if 10s if not 100s of your students are asking for a simple answer document for your problem sets so they can confirm that they are grasping the content correctly as they cannot attend office hours for a multitude of reasons, maybe reconsider. The lectures also left a lot to be desired, as he would spend about half of the hour lecture answering questions that could easily be left to Campuswire, and the other half zooming through content that is sparsely detailed. He would be willing to spend an entire class on a derivation only to reveal that it wasn't content we needed to know but spend only a few minutes on concepts that were entire questions on an exam.

In summary, this class sucked. I wouldn't recommend taking it if you have the opportunity to do literally anything else. But, I think (and hope) that with time and actually listening to the students Barr could do better. It's clear that despite his shortcomings in translating it to the students, he has good knowledge of the content.