This class was supposed to be titled "Chemical Energetics and Change"
But what actually taught by Weiss were:
x-ray photoemission spectroscopy, x-ray diffraction crystallography, flow cytometry, fluorescent in-situ hybridization, silicone polymers, biopolymers, direct and indirect-band gap semiconductors, semimetals, semi-insulating semiconductors, and so on.

And yes, as you expected, these topics are designed not just for fun - they DiD appear on the exams, which were purely conceptual (no calculators were allowed, by the way, because there were NO questions involving any quantitative calculations). While the topics that were supposed to be in the syllabus - entropy, enthalpy calculations, acid-bases, kinetics, etc. were barely covered during lectures, which appeared to as highly incoherent, disorganized and strangely paced ("flow of consciousness" should be a better term) as a typical episode from Rick and Morty - that is, you never know what's coming up next.

I would recommend Weiss to all kids who are chemo-nerds/maniacs and enjoy bragging hours after hours about nanotechnology. However, if you intend to take chem20B to gain some true, fundamental and organized knowledge of chemistry, Weiss would never be your first choice.

We can see some pretty words coming from the latest review, praising Prof.Weiss for the "challenge and tests that conceptually prod your understanding of chemistry to previously unattained depths". Indeed, the materials covered during lectures are interesting and unprecedented. However, I would like to ask the reviewer:

"Did the extra course materials compensate for the loss in materials that were supposed to be taught but not covered in lectures?"

No they didn't. Weiss didn't really discussed much about thermodynamics, acid-bases, or equilibria. As a result, you have to study them on your own by referring to the textbook, which is indeed poorly written.

As an introductory course, chem 20b is designed to prepare undergraduates for their even tougher upper division chem/engineering courses. Thanks to Weiss, I can say that over 60% of the class became underprepared.

I do not want him to overthrow this course's original aim.

This class is almost entirely about Weiss' nanotechnology research and techniques more than about what supposed to be Chem20B materials. It got three midterms - lowest one dropped, and a final. You will be tested on those research as well, along with some weird grading criteria - it is like grading an essay. There is no calculation on the tests, it is conceptual and confusing - almost like a guessing game. The way he teaches lectures is like research talks, however the students, with very little background knowledge, have to "imagine" of what he is talking about. There are some days lectures will be on Skype, which is not helpful at all. I studied countless hours and still messed up in this class. Paul Weiss is a great researcher and a nice guy, but I definitely do not recommend this professor for Chem20B. Find another professor who will make you love and enjoy Chemistry.

I loved this class. My friend and I referred to it as "Storytime" because every one of his lectures was just him talking about funny stories and things about chemistry he thinks are interesting. That made the class super interesting and easy to make yourself go to. He's a funny little dude and what he teaches, he teaches well. However, he teaches pretty much none of the course curriculum, leaving that to the homework problems. So if you want to actually learn 20B, don't take him. But if you want to enjoy the class, Weiss is your man. You hardly need to take notes if you pay attention to the lectures and go to review sessions before tests. The tests aren't hard at all if you do that, plus there is a ton of extra credit available. It's annoying that he gives a ton of homework and it's due every lecture, especially since it's always on topics totally separate from the lectures. But all the test material comes from the lectures, not the homework, so it's not a huge deal. Overall, there's more work than there should be and you won't learn anything that you're supposed to, but it's super easy and even more interesting. I would recommend this to anyone who needs to take 20B but isn't any form of Chemist.

This class is very frustrating. Dr. Weiss was so busy and had no time to prepare the lectures. As a result, the lectures deviated so far away from the course description. It's a total waste of time to go to the lectures.

You can never tell how you're going to do on the tests. The TAs have very vague reasons for not giving you points because I'm assuming Paul Weiss just gives them a few keywords to go off of. This class was a great learning experience and was inspiring and optimism inducing, but overall it's incredibly frustrating.

Chem 20B with Weiss is very very different than with Li. It's really not fair how different the two classes are in terms of difficulty. Weiss goes over at least three more chapters than Li does and his grades are much lower than compared to Li. That being said, Weiss is a fantastic person and extremely helpful, but his class is very frustrating. There is homework due each lecture, accompanied by around four sections in the book each time. This homework often takes a 1.5-2 hours if you do all the reading. The homework is graded and counts for 30% of the class. While most may see this as a good thing, the TA's almost always handed out 2/3 for the homework, which means you're losing 10% off of your final grade. In addition, the reading and homework have nothing to do with what is covered in lecture. It's like taking two separate courses within one. The homework is mostly equations and numbers-based, while the tests are entirely conceptual. It makes no sense. I can see how a chem or biochem major would enjoy this class, but as an engineer who just wants to fulfill his chem requirements so he can move on, this class was very unenjoyable.
TL;DR Only take this class if you really love chemistry. Otherwise, take Li. Actually, just take Li no matter what.

Taking Chem 20B with Weiss was probably the worst thing I've done at UCLA. My motto is "KNOW THE MATERIAL SO WELL YOU CAN PERFORM IT IN YOUR SLEEP". I did that for hos class, too. I did the all-nighters, I put in 60+ hours of study per midterm (3 in his class) enough to make you feel prepared, but no, the midterms were wholly focused on things that shouldn't even be in the 20B syllabus.
He had homework due EVERY lecture, and most times, the TA's would give you 2/3, leaving you with a C average on the homework, which was worth 30% of the total grade.
The final exam included material that did not have anything to do with the course.
Coming from a big time chem lover, if you still want to like chem or even pass it, take it with some other professor. Weiss is a nice man, but you can tell he is more of a researcher than a professor.

I learned a LOT in his class. He's such a sweetheart, but homework is worth 30% of the grade, and it's due every lecture. If you love chemistry, you'll love Weiss. If you hate chemistry, you'll hate Weiss.

That said, your experience is based mostly on your relationship with your TAs. If you get his class, PLEASE PLEASE make sure that you get a good TA. I got lucky, but I've heard horror stories about TAs who refused to change the grade because, although he wrote the right answer, she didn't feel that he got the answer right.

Get a good TA, do your homework, ask Weiss something about semi-conductors, and you'll get an A. Guaranteed.

Even Weiss himself recognized that Winter 2016 was grueling, so he modified his class waaay more so that it was actually doable lol. A lot of the old reviews scared me so much after I got stuck in his class, but honestly it wasn't so bad. My biggest complaint is the workload, since homework was due every lecture, but didn't actually help much for tests (homework was book problems so very quantitative, yet we couldn't even use calculators on exams). Weiss is obviously very knowledgeable in his field and likes to name drop a lot of distinguished people with whom he's worked with (awe inspiring or yawn inspiring is up to you lol). He takes feedback pretty well, and even though I was a bit annoyed with how he designed his class, I do felt like he actually cared about the students. He often did reviews before midterms/ the final, as did his TAs, which were immensely useful since it was easy to get confused during some of his lectures (he gets excited easily and goes on tangents, especially if some students asked some non sequitur questions). If you go to the review session and review his recaps and such you should be fine. The only curveball I didn't like during exams was in the first midterm when he asked about acid/base stuff although we barely covered it (this should tell you that Weiss likes to preview new stuff in his midterms so beware and study more newer stuff than older stuff)
Like the person below said, however, Weiss did mention that the next time he'd teach this class is as an honors class, which makes sense because I feel like only the really passionate chem people would put up with the amount of work he has you do. Overall, he's kind of a funny uncle type of person, but he really does know his stuff