Regan is...interesting. He skips the Physics 17 review that's scheduled in the beginning of 115A and focuses on special relativity: his favorite. As you make your way through 115A with Regan, you'll see that he has a problem with h_bar, energy, momentum, mass, and Griffiths. Anyway...here's a longer breakdown:

1) He assigns a lot of homework. Problem sets are mostly from the textbook (which is good), but the Regan specials are a hit or miss. His lectures are not that helpful for the HW (as he kinda just talks about what he finds interesting), but once in a while (maybe the day before the HW is due), he will say some useful stuff for the HW. He expects you to read the textbook (without telling you to read the textbook), so read and do the HW.

2) His exams are...interesting. If he gives a question similar to the textbook, be sure to get full points on that. The Regan specials are hard to do. Most of the time, I'm not sure what he's asking on his questions. If you can reach him during the exam to get clarification, please do so. HIs questions aren't necessarily impossible, but they are just worded confusingly. If exams were in-person (or synchronous), I would've asked for clarification and scored better. His curve is nice though, so that's good.

Overall, Regan is a funny guy. He's very likeable and is happy to talk to you about almost anything during office hours. He loves physics and he wants you to love physics too. But, his exams weren't that good and he thinks we can work faster than we actually can. If you have to take Regan, it's not the end of the world (as his class was kinda fun), but be prepared to do some work.

Regan's such a cool guy. He loves QM. He teaches you to appreciate a more elegant formalism of physics that used wavenumbers and frequencies instead of momentum and energy. Tests are moderately hard but generally exciting. Homework is long and generally not that fantastic. He also covers relativity in an abstract, linear algebra-heavy, but informative manner. It's hard but rewarding.

Take this class. You'll love it, and it's worth the work.

Regan is a cool dude and liked to joke around a lot. The tests in this class are pretty difficult and the homework often took forever to complete. Regan also likes to start the class off with special relativity which was surprising to say the least. In fact, the SR in this class is harder than what I did in 105B but it was admittedly more helpful than what was done in 105B. After that, though, the class was what you'd expect out of a QM class.
Also, the curve in this class is fucking great so that always helps.
Overall, the class was genuinely fun and I would recommend taking a class with Regan if you get the chance.

I think this professor has unrealistic expectations for what should come obvious to students. I think the materials in the class (textbook, homework, aside essays, tests, etc..) are fair and help one learn what they are supposed to for this class. This class was very fast paced in content but also had a manageable workload. Although I found prof. to be a very entertaining lecturer and great at explaining concepts, I found myself uncomfortable asking any questions for the fear that they might be seen as trivial or obvious. I would have appreciated more explanation for where many of his lecture derivations come from.

I feel that Regan has a lower rating than he deserves because his exams are difficult. He really does care about students doing well in the class, which is why he curves so much.

HOMEWORK: Some questions are hard, some are just plug and chug. I really like the questions Regan writes, and I wish he wrote more of the homework questions because they usually take a while, but I come out of it with a deeper understanding of the topic of the question. They were graded on correctness, but I feel they graded pretty easily, and the TAs were nice with regrades.

EXAMS: Honestly, they were all reasonable in my opinion. There were definitely difficult questions, but a lot of the problems were straight off the homework, or straight from a derivation he does in lecture that he makes sure we know is important, so make sure you understand those. Also, when I say some questions are straight off the homework, I don't mean the plug and chug problems. I mean the problems that really get us to think about the concepts at a deep level. Sometimes, he will even tell us that a certain topic is definitely going to be on a midterm/final.

OFFICE HOURS: Sometimes they're helpful and sometimes they're not. He will go over homework problems if you ask him about them, or at least get you started on them.

COURSE CONTENT: Although I personally didn't hate how Regan structured his class, it isn't for everyone. His lectures focus more on what he thinks is important for a physicist to know, which I actually like. However, his homework is mainly questions from the textbook, and he often doesn't talk about the content covered in the homework until the lecture on the day the homework is due. Because of this, the homework is often self-taught. The tradeoff is that you are able to learn certain things that other professors would not have taught. For example, I don't think statistical mechanics is usually covered in this course, but Regan talked about it for 2ish weeks before we did any quantum. Regan also curves the class at the end rather than each test, so it's hard to tell what grade you have during the quarter. This is a big factor of stress for students, but I feel that Regan acknowledged that this quarter and is trying to make easier tests now so the averages aren't super low.

Overall, I would recommend Regan because he is a very entertaining person, and he does care about students learning the content.

Professor Regan is a great lecturer and makes his passion for physics (as well as his hatred for arbitrary constants and units) very evident. He'll clarify a lot of the language and fluff that cloud the overarching concepts behind basic stat + quantum mech. Things may feel a bit confusing in the beginning but once you reach the end of the quarter it should click.

The problem sets are generally doable with what you learn in lecture and he's pretty generous with extensions if you guys ask. Make sure you really understand the homework well because he can (will) use similar (identical) problems in the midterms/final. Pay especially close attention to the problems your TAs emphasize in discussion or office hours and you'll do well on the exams.

TLDR: Lectures > textbook. Put effort in problem sets. c = 1. The Planck and Boltzmann constants, among others, are sacrilegious.

The professor drops a lot of formulas throughout the class. While he often does not give explanations as to where they come from, he will explain them in his office hours. Reused questions from the homework for midterms and questions from the midterms for the final. Going to class is essential.

This class took away any doubt I had about majoring in physics. Regan started off at a hundred miles an hour with geometric algebra and stat mech but backed off quite a bit after the first midterm. The first 3-4 weeks were absolutely terrifying, especially since his lectures moved incredibly quickly. Don't try to take notes during lecture unless you already have some understanding of what he's talking about - he complained a lot about the textbook but ended up following it pretty closely, so try to at least skim the section before lecture. The class slowed down a lot after midterm 1 when we got into the background and very basics of quantum, which was by far the easier part of the class.
He assigned a lot of homework but was very forgiving with deadlines and his exams were very fair. Learn the homework well and you should be fine for the exams, many of the problems were similar or identical to ones we had already seen. Also, don't expect to get much homework/content help from office hours - Regan would always start off trying to answer questions but would quickly get distracted and go off on tangents about his own interests. This ended up being my favorite part of the class and I would highly recommend going, he brought up so many little things that made me even more interested in physics. He has a thing against the cross product as well as hbar and other "fundamental" constants like c and the Boltzmann constant and prefers to describe everything in terms of frequencies but he won't force that on you in exams. In summary - Regan is a little crazy and makes you feel like you have no idea what's happening but taking it with him is absolutely worth the extra effort, at least it was for me.

This class was very difficult and the curve is not generous.

Professor Regan knows his stuff, and that's an understatement. He clearly has an extraordinary grasp of quantum mechanics and does his best to impart that to students. There's two downsides to this, though. The first is that it makes it hard for him to realize that students may have some difficulty with the concepts. They might be second nature to him, but they're entirely new to us. Yet he assumes that we are as comfortable as he is, and races through topics like the goddamn Road Runner getting away from Wile E. Coyote. The other problem, though (and this is arguably the worse of the two), is that Regan's self-perceived mastery of physics makes him an insufferable asshole. Just absolutely so far up his own ass, he's basically wearing his head as a beret.

With that said, I will reiterate that Regan is very knowledgeable, and he does at least try to share that with his students. Sometimes he goes a bit too far and too fast, but it's clear he is making an effort, which I appreciate. And it works. I do feel like I have learned a good amount in this class, that I may not have if he had not focused on the fundamentals like he did. In addition, his exams are insanely difficult and nearly impossible to finish in the allotted time, but he seems to be fair about grading and curving them, so the end result isn't too bad. Moral of the story then: really smart guy, raging asshole, medium teacher overall.