Of course it's a lot of work, but it's satisfying work if you do it. Really great class for prospective any prospective chemistry-related majors. Weiss also cares a lot about your learning and is really nice guy. You won't regret doing this class.

Pretty shocked at how low his 20B reviews are. He's probably my favorite professor. Maybe if you're a tryhard, he's the kind of professor for you. He places a lot of emphasis on putting work into getting good grades - it's really hard not to do well if you try.

***I took this class in an online format during the COVID-19 pandemic. TL;DR at end.
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This class is a lot of work, but ultimately, it's an experience that's worth it. If you're deciding between this class and CHEM 20B, I believe you will have a better time in this class, as long as you're willing to put in a bit of extra work. It will save a lot of stress and worrying about poorly written exams or such.
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The homework in this class consisted of weekly problem sets, assigned from the textbook (which you can find online for free). These would usually be somewhat related to the lectures in class, but in general, seemed supplementary rather than complementary. Another weekly assignment was to design your own problem about a topic from the week, which is pretty simple. There's also the "Literature Assignments" — you choose a research paper on a given topic, and write a short summary. It's pretty time consuming, but it's a useful skill, and the grading on all three types of assignments is very forgiving. Your lowest score for each is also dropped. There's a large project in this class, where you choose some topic related to the class and heavily research it and make a poster and presentation. It is a significant amount of work, but it's also not difficult to do, and you get to choose your topic, so it's interesting.
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Lectures and discussions weren't exceptional, but they're certainly useful. Paul is a great guy, very nice during lectures and office hours. He's pretty easy to listen to and understand, and never makes it hard to ask questions. The class is also much smaller than other similar courses, so if you're somewhat active in participation, he'll know you personally. Participation was technically part of the grading, but I think that just meant "show up to classes and talk at least once throughout the quarter," so free points, really.
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The midterms were very fair, and also were 50/50 individual/group performance. After the individual section, you were allowed to consult with the whole class, and basically get a free 100 for the group section. Each midterm had a pretty significant amount of extra credit too. The final exam is an oral exam you have to schedule with Paul individually, but the questions are basically the same, he just asks you them in a call. That may sound bad, but you can just ask him for hints if needed, and he's super generous on the grading. If anything, the final is one of the easiest parts of the class. It was super nice to not be stressed about the final when I heard CHEM 20B students freaking out about theirs.
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Finally, there's tons of extra credit opportunities. There's an extra auxiliary lecture you can attend and do an assignment on for I think 2% of your grade, and the midterm extra credits were pretty significant too. I think most people reading this are just considering this or CHEM 20B, so here's the comparison: CHEM 20BH is more work and requires more self-interest/initiative, but is much less stressful and more inclusive since the class is smaller.
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Point distribution (there is no curve on exams or the whole class):
Midterm 1 - 10%
Midterm 2 - 10%
Final - 20%
Project (5% poster, 5% presentation, 10% paper) - 20%
Homework (10% creative problems, 10% textbook problems) - 20%
Literature Assignments - 10%
Auxiliary Lecture (each after the first is extra credit) - 5%
Participation - 5%
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Basically, only 30% of the class is individual exam performance (b/c of the group phases of the midterms). It's not too difficult to get an A since there's so many other assignments.
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TL;DR: If you're confident in chemistry (taken AP chemistry or a similar level class) or are willing to spend some time reading the textbook each week, just take this class. It's a much better experience than CHEM 20B, plus you can save it for second enrollment since it doesn't fill. If you're still not convinced, go read the 20B reviews for Barr, who was the option for Winter 2021. Or even 20B for Weiss, the same professor.

If you've taken AP Chem, then this class should be fairly easy. The content does not extend very far beyond AP Chem. The test difficulty was fair. Additionally, like others have mentioned, midterms are split into 2 parts: the in person solo phase, and the take home group phase, and you're basically guaranteed full credit on the group phase. The in person part of the exam is also open book, which made it fairly easy as well.
In terms of workload, I personally didn't find it to be super ridiculous. There's one homework assignment per a week based on textbook problems and some problems he wrote, and every so often there's a literature assignment (I had 5 so it's basically every other week) where you read a research paper and summarize it. You'll see a lot of reviews complaining about the final project, but that project has been modified. Currently, the project entails a poster, a 3 minute video presentation, as well as a 1 page analysis on how an AI summarized your topic. So the only real writing you have to do is the script for the video and the analysis on AI, which I personally didn't think was that bad.
If you want to get into research (which I assume you do if you're in STEM), I highly encourage you to take this class because it makes you practice a lot of research skills that you didn't think about. Reading and actually comprehending a research paper, for example, is very much an acquired skill (at least in my opinion) and the only way to hone that skill is to read more research papers. Paul also encourages people to show up to research seminars and there are extra credit questions on tests related to them. But even without the extra credit, I think going to research seminars is a good habit for researchers because you get to learn about current frontier research from the very people pioneering those projects.
My main/only criticism of the class is that I genuinely did not find Paul to be a super engaging lecturer. He tends to go on tangents about how he is personally connected to the scientist relevant to a concept taught in class. While it is interesting, I do find it to be a bit much sometimes.
But overall, I did enjoy this class, and would highly recommend it to anyone interested in doing STEM research.

The workload for this class is A LOT, but Paul and the TA Katie are extremely generous with the grading. Most of your grade isn't dependent on the tests so you can get the lowest score on the midterms and still scrape through with an A like I did.

The class itself is really research-based/heavy, and you become really research literate by the time the 10 weeks are up. Going to Paul's office hours are a must if you want to join a research lab, as he will give out recommendations left and right for the students who took his class.

This class was genuinely enjoyable. I loved learning about the broader concepts and applications of chemistry, and it really helped me grow in how I think as a scientist.

That said, you cannot afford to fall behind. The workload requires constant attention, and attendance Monday through Friday makes time management challenging—especially if you’re taking other classes. It’s demanding, but also very rewarding.

Paul grades fairly (if not somewhat leniently), so I wouldn’t stress too much about your grade as long as you stay engaged and find some interest in the material. Exams (midterms and final) focus on applying concepts rather than throwing unexpected curveballs, and they’re open note—which helps a lot. I printed everything, though I ended up using very little of it during the exams. Overall, a challenging but fulfilling class—enjoy it!

Paul Weiss is one of the worst teachers I have ever had in my entire life. This man has no regard for how well his students actually learn. If there are other options for teachers in this class, take them. If you have the flexibility to wait a quarter and take it with a different teacher, do it. DO NOT TAKE HIS CLASS. During the class I heavily relied on my friend who had taken 20B a quarter before with a different professor. About halfway through the quarter we reached a point where she could no longer help me because we were learning stuff that wasn't even apart of regular 20B content. The entirety of that sentence alone should be a red flag enough. But to actually get in to Paul's teaching style, the bottom line is he doesn't actually teach. Each class I would try to pay attention and learn the content, yet each time probably 5 minutes in we reached the inevitable point where he would go on a rant about some medical device that his friend created or about his friend that he's about to go visit that has a noble prize or their own lab or is doing this great research. While normally I can appreciate a little bit of getting sidetracked, as it can make the content more interesting, his getting sidetracked has the exact opposite effect. He would go on for so long about topics that have nothing to do with the class it gave no chance for us to actually learn anything. Additionally, his lectures consisted of a series of slides, each composed of a long bulleted list of topics. He would proceed to "explain" the topics, but most of the explaining was what I described before, bragging about his cool friends and his personal life, or medical things that the majority of the class had no interest in knowing, or need to ever know. Because of that I stopped going to lectures a few weeks in. A week before the midterm I decided to go and see if we would actually learn any content (spoiler alert: we didn't), and I counted how many students were actually present in class. Out of the at least 120 students taking the course, 40 were present. That just goes to show how bad of a lecturer he really is. Now you may be wondering about homework and tests and the rest of the course. Surprise, they're just as bad. Each week he would assign homework that would take an insane amount of time, that also had NOTHING TO DO WITH ANYTHING ELSE. Several times he stated that the lectures, homework, and readings were "complementary." They are anything but that. Put together they made no sense and made it impossible to actually know what content we needed to know for the exams. While both the midterms and the final were all open note, it doesn't matter. The tests would ask the most convoluted questions that he said would test our intuition. Shocker, I don't have the same intuition as someone who has been studying chemistry their entire life, and have only ever taken two other chemistry courses. Also, don't expect your TA to be of any assistance during this class either. In my discussion of at least 20 people, 4 of us regularly attended. This is because any time we asked a question about the test, or about the grading of the test, the reply was "I don't know, you would have to ask Paul." All in all, please do not take his class, it's not worth the extreme headache and time wasted. I wish I had just waited a quarter to take it with a different professor.

Most people feel relieved when they hear an exam is open-book, but not in Weiss's class. I genuinely do not understand how some students enjoyed this course with him. Without exaggeration, this was the worst class I have ever taken. No matter how many hours I studied, I never really knew how I did on the tests. Lectures aren’t recorded, and the modules are just slides with random, disconnected topics. The textbook doesn’t match what’s covered in lecture, and the discussion worksheets don’t prepare you for the exams at all. To be fair, I’ll give Weiss credit for being flexible and offering a diverse grading structure. Other than that, this is not a typical chemistry class, and I would not recommend it to anyone. I regret taking it with him.

Paul Weiss is a horrible professor, and I say this from the deepest place in my heart that I truly hope he never teaches another Chem 20B class ever again. It is clear from his lecturing style that he should remain behind a desk and continue to do research. His lectures consisted of slide shows that had bullet points with some important sentences, but mostly pictures of him with Nobel Prize winners. He would start on the topic at hand, then always ramble into tangents about a "funny" story of his old teaching days in Chem 20BH or an inventor he met in his free time. He claims that the homework, textbook readings, lectures, and discussion worksheets are "complementary to each other," but they are incompatible as the discussion worksheets were way behind the content we were "learning" in lecture, and the homework was so far ahead of the lecture content that I resorted to learning everything I had to know from the textbook and yet that still wasn't enough. When asked questions, he avoids giving a straightforward answer and is often quite patronizing. He kept saying he was preparing us for standardized tests in the future, like the MCAT, but this is general chemistry, where half the people taking it are engineering majors, who will not go on to take more chemistry or these tests he talks about and "prepares" us for. For the first midterm, we were blazing through topics that should have lasted us until the end of the quarter, and got so far that for the second midterm, we went outside of the scope of Chem 20B. If I wanted to take an organic chemistry class, I would have.

Furthermore, my TA was of no use when I asked him questions about the class's structure or the content that would be on the exams; he often said, 'I don't know' or 'I don't know why Paul Weiss does it like that.' Not only was Paul Weiss an inept lecturer, but he also asked the most mind-bending questions on exams that he expected us to know, when he never taught us that content. Although the exams were all open note, that is not an excuse to make the midterms 2 hours long and ask the most ridiculous questions that are all free response. Safe to say that Paul Weiss did NOT prepare us well for any of the exams, and I feel bad for his TAs and LAs who need to pick up the slack for his pathetic excuse of a review day. I would have much preferred to take a normal Chem 20B class where I wasn't constantly being given material from a previous Chem 20B Honors class that he taught in 2017. Lastly, Paul Weiss was so busy with his research that he would often leave town to attend forums and leave us with a sub which would have been a blessing except he left them a set of slides to go off of, which were just as useful as if he were to cancel the lecture all together.

Please, UCLA, never ever let him teach Chem 20B again. Instead, I think that the whole class would have preferred to take it in the fall with an actual qualified professor.

Ok this is somewhat incomplete seeing as I couldn't even complete his class. In full honesty, even though I dropped this class week 4, I still attended some of his lectures with my friends because this guy is definitely a character.

His class is basically all a bunch of different topics going on at the same time, and the expectation is that you learn all of it completely and effectively. What I mean is that all of the reading, the homework, the lectures, and the discussions were all disconnected from one another, but the midterms were comprehension based that combined every piece of material.

I would agree with the rest of the reviews that Weiss is kind of arrogant, however I really liked this about him. I would rather have an arrogant and engaging lecturer than someone who had no idea what they were talking about. He was pretty funny, and if you paid attention what he said didn't seem too crazy or outlandish. He just covered supplemental material during lecture, so it was pretty hard to make up. This made it pretty difficult because I had to miss an entire week of class due to personal reasons.

Anyway, the main complaints: homework was pretty time consuming considering that we wouldn't cover any of the content during lecture. Weiss was also really proud of the fact that he taught 20BH, the honors version of the class. As someone who took all of the honors physics 1 track, it made me laugh that he was always talking about how great that class was and how special they all were. I didn't feel affected by it, but it definitely could be bothersome to people. His lectures tended to go in places that didn't feel relevant but definitely were, so if you weren't paying attention it was harsh when it came time for midterms. The midterms were also held after lecture, so you had an extra time commitment which was kind of annoying.

pros: Weiss is entertaining as shit and if I wasn't graded in his class I would've loved it. The homework and discussion worksheets had higher weight in the class than the midterms, so if you messed up it was okay. Tests were completely open note, so you could've brought a lot of material to the test. I would say this class is somewhat comparable to an honors class, so if you're a chem major I would try and take Weiss because he's definitely a good contact. He promised basically everyone in the class research.

All in all, don't take chem 20B with Weiss if you just want a standardized chem class because it's a lot more than that. Just take 20BH if you want, or wait til you can get an easier prof.