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.

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.

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!

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

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.

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.

Flatulants on the road
Ghostracers chasing lost souls
Got myself a coffee
Spilled some on my shirt

USC grads make no dollars
I and Carey are bad spellerz
Memory leak is wrong wrong wrong
For this project, you do not need to submit a report. You're welcome.

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.

Just here to boost lil berg's stats.

Smallberg is a clear and helpful professor. He is open to questions, and is basically a walking CS dictionary. His lectures explain stuff very well.

You will learn a lot in CS 31, especially if you have no previous experience. It is rewarding, but if you have no prior experience, it will be very hard. His tests have a strange format that takes getting used to, and I got absolutely hammered on the first midterm, scoring below the 25th percentile.

I also spent more time in CS than the rest of my classes combined, which were Math 32B, Physics 1B, and Chem 30A. CS 31 is no joke if you're not a CS major.

He curves generously, but people still get hammered in terms of GPA. CS isn't an easy tech breadth, and you should think before choosing a CS tech breadth.

Finally, the book was kind-of useful.