For the class that most math majors consider to be the most difficult, it wasn't too bad. The weekly problem sets were doable with the small study group my friends made. As for the midterms, only 1 out of the 5 questions was a full-out proof that most people in the class struggled with. Chernikov himself really seemed to care about teaching and although the lectures were not extremely engaging, his one joke per lecture was usually pretty funny.

Prof Chernikov is a cool guy and I really enjoyed his math 115B class. During lecture, he teaches straight from the book. This was a good and bad thing in my opinion--good because I could re-read the book after lecture to ingrain the concepts in my head, but bad because I hate Friedberg's Linear Algebra book. Maybe I'm just not good at math but I really think that book is horrible. Anyways, Chernikov is funny and good at explaining concepts. He does go kind of fast, but its easy to go back and learn what you missed.
As a class, I would say 115B is fairly challenging, but that's what made it great. If you have the chance to take 115B, take it. And if you can get a class with Chrenikov, do it.

I took this class (online) spring 2020. Chernikov is a good lecturer, but not an exceptional one, but IMO the way he sets up his class makes it the best class I have taken so far in this online environment.

Firstly, he published all his lectures on youtube (https://www.youtube.com/user/archernikov) beforehand, and then during scheduled lecture hours, he just went over HW problems. Also, he types up all his notes on Latex, and they are really neat, so it's not really needed to even watch the youtube lectures, instead it's possible to just glean enough information from the notes he publishes.

However, the lecturers/notes are not very helpful when compared to the homework he gives. He gives 8 homework questions a week, and they are incredibly difficult. Even with online resources and friends, the averages on these homeworks consistently ranged around the 70/80% range (the TA grading was also exceptionally difficult). The saving grace is that Chernikov gives hints on the homework in his scheduled lecture hours (which are just extra OHs), and then he records/posts the videos on CCLE. Most of my friends in this class stopped even trying to do the homework before thursday or friday, since without Chernikov going over the HW problems, they are basically impossible.

The textbook is freely available online, but it's not that helpful. Online resources are often more helpful. He takes a lot of HW questions from Rudin Real Analysis, so if you get an answer key for that, it's quite helpful.

Exams are easier than HW, but not much easier. Each took me about 6-8 hours to complete (but I was being really careful to complete everything correctly due to the harsh grading by the TA). If I took the tests in person, I would probably get around 15% on the midterms and final. They were that hard!

As much as I complained about this class, however, I learned a lot. Chernikov's homeworks are pretty different than his lectures, so it's not necessary to go to lecture, but instead forces you to actually understand the content by doing the homework (learn by doing philosophy). I would say the homework was too hard if he didn't give hints, but with hints, the homeworks were definitely reasonable. I also enjoyed how the homeworks often referenced old material; for example, for homework 6, you would have to refer to week 5, 4, 2, and 1 notes.

Ultimately, this class is fairly difficult, but Chernikov is an excellent professor to take it with. He really cares about his students, but also makes sure that you actually learn something in the class. Also, I think Chernikov has adapted best to the online format at UCLA due to COVID-19. So if Chernikov is teaching a class online, I highly recommend you take the class with him!