Smallberg seems to have plenty of reviews already that give a pretty good gist of him and the class. Here are some things I'll emphasize:

1) He does an excellent job of teaching the material, showcasing every detail, and making sure the class can follow along with him.
2) His lectures can get very dry, especially since they are almost two hours long.
3) He does not use slides. He just writes out different programs that illustrate what he wants to teach the class. This worked for me as it showed me the actual application of each lesson, but it requires you to take good notes.
4) Midterm 1 and 2 were combined this quarter and it was fairly easy with around a 90 average.
5) Final was more difficult than the midterm but still manageable. Average was around an 80.
6) Projects aren't too bad but there are a lot of them (7 in total) so just make sure to manage your time properly.

Had taken CS 31 and CS 32 virtually with Smallberg. He does not usually use slides, he sometimes writes codes in Word, and the lectures can get boring. BUT STILL, he's an absolute legend and a wonderful man. Let's boost this man's rating.

Smallberg is a legend. I'm just here to add to the abundance of reviews for this beautiful man.

Dear professor Smallberg, I can certainly see why you received so many compliments in previous years. You are a great lecturer, making everything super clear. Your assignments were fine, some of them are very interesting.

However, you are irresponsible. On week 10, we only get 4 out of 9 assignment grades, and the midterm grade was missing as well. Then, based on the first 4 assignment grades, you tell me my "estimated grade is B+". That's 2 HOURS before the deadline for changing grade type. So I changed this course to P/NP. Then you released the rest grades, I got 100 on all of them. At the very end of the quarter, I still do not know my midterm grade nor my final exam grade. You promised you would post the grade, but you didn't.

I won't complain at all if I screwed it up myself. But your irresponsibility leaves my grade with a question mark. I received a P, but I had been wondering if it wouldbe A- or an A if I did not change the grade type. Incomplete information about grades is just RIDICULOUS.

Though Smallberg was quite slow on grading (thanks to his dual 31/32 teaching workload), he was an effective and thorough lecturer. Overall the content was far more interesting than CS 31, with the homeworks and projects not being terribly difficult (concept wise). Since the content pacing was kind of slow, reading Nachenberg's slides helped a lot. Project 3 was a huge time suck, but good enough planning (and starting early) made it mostly manageable in the end. Due to COVID, the midterms were a weird single question format, and the final was made no-harm (though it was significantly harder than the midterms). TAs and LAs were helpful and responsive. Good luck!

If your correctness score is 60 or below, it may not be because of a lack of
understanding of C++, but something more fundamental: You ignored
repeated admonitions in the spec and in class to avoid specific foolish
mistakes, yet you made them anyway. Whatever your field of study is, you
must fix this characteristic about yourself. No employer would dare hire
someone who ignores repeated spoken and written directives: You'd pose a
risk to the safety of yourself and others if you ignore safety rules, a
risk to the financial health of the company if you ignore legal regulations,
and a drain on productivity if your ignoring specifications causes you or
others to devote more time later on to correct your mistakes.

What's exasperating is that despite all that was said above, there will be
people who will ask for a re-examination of their correctness score
without saying which test case numbers to look at or without having tried
those cases under multiple compilers or without running the Project 2
tester mentioned in FAQ #7. Those people are exhibiting the exact
characteristic that may have caused them to make the mistake that cost
them so many points: They don't pay attention to what they read.

小宝讲课用来学习，南宝讲课用来下饭

Smallberg is an absolute legend. He probably knows more about C++ than Bjarne Stroustrup and Dennis Ritchie (whom he mentions a lot). This is class is one my all-time favorites! It's also quite easy if you're willing to put in the effort with a good attitude. If you took AP CS in high school, you're chilling.

A lot of people were ragging on him for being slow with grading this quarter (Spring 2020), but objectively that's a pretty minor consideration when you're evaluating the effectiveness of a professor. Smallberg teaches the class very well. As a lot of reviews have already said, he's not the most engaging lecturer due to how much he pores over the details, but if you pay attention, you'll find that he really does such a good job explaining concepts. I always came out of lecture understanding a new topic pretty well.
There's obviously a lot of complaints about the workload, which does get pretty heavy after week 6. But it's NOT unmanageable. Yes, Project 3 is extremely tedious and does take 20-30 hours to complete, but we get two weeks to do it. If you plan properly, you'll be fine. Smallberg was actually lenient this quarter and gave a relatively easy Project 4, and yet people still love to complain.
Honestly I don't get all the hate Smallberg gets. This dude works harder than any professor I've ever had. He designs unique projects each quarter for CS32, and that means he also has to come up with new test cases every time. Grading in this class is a more intense process than others, so it's obviously going to take longer than other classes to get grades back.
Overall, I would definitely recommend this class with Smallberg. I never attended Nachenberg's lectures so I can't give a comparison, but I will say that this class with Smallberg taught me a lot, and is a very valuable class to have under your belt.

I must say, Smallberg is NOT the hype that he is made out to be. While he is obviously a brilliant professor, extremely knowledgeable about the subject matter, and has his engaging moments, there are a few notable caveats in his teaching style I want to draw attention to. (Note: if you're a first-year CS or EE major, you basically have no choice but to take him, as he is the only professor for CS 31 in fall).

Smallberg uses a flipped classroom style of teaching. He does a meticulous job of prerecording an entire quarter's worth of lectures that you watch on your own time, and the listed class time is spent in Q&A sessions. While I can see how some may like this, I thoroughly hated it, as the lectures were sooooo dry. In Q&A sessions (think about them like 200-person office hours), Smallberg is actually pretty funny: at the direct expense of an unfortunate few. He is not afraid to humiliate you in front your hundreds of peers if you ask questions that he deems "beneath" him, to the point where I would feel uncomfortable asking questions (even through I was fortunate enough to never be directly called out by him). It doesn't help that the class is 80% men, so I can only imagine the impostor syndrome my female peers could potentially have felt. Additionally, grading and curving is BRUTAL. The class is a war of attrition. There are no defined cutoffs for specific grades when the class begins; your projects and tests basically go into a black box that gives you a letter grade at the end of the day, so hoping and praying is the name of the game. Everyone is so smart that even the extremely difficult final was not curved. Despite getting a solid B- on the final, I was lucky enough to scrape by a 93%.