After his first quarter of teaching he had good reviews; overall he was sitting at around 3.8 or a 4+ or something in that range. *He looked good*. Hence why so many people eagerly signed up to this class. It takes a lot to drop from such high reviews to such low reviews.

He angered a lot of students. Not just some of them. Practically everyone in Spring 2019 had a bad experience in his class. I could go on and on about this, but I don't need to. Just read these other reviews if you want an idea of this monstrosity.

I took this class in the online format in Spring of 2020. I learned a lot in this class, Professor Rosario makes the content interesting and is very helpful during office hours and on CCLE. On CCLE, he will give extremely clear answers which was really helpful especially due to the online format of the course. During office hours, he is approachable, and I was able to get clarification on some of the harder homework problems.
In addition, towards the end, he covers some topics that are not required by the curriculum but are very interesting and useful. He also gives advice on his experiences from industry etc in the last class which was awesome to hear especially since he is a UCLA alum.
Exams are challenging, and reflect lecture and homework content. The homeworks were reasonable although they usually had a couple of difficult questions that usually took a little more time.
I highly recommend Rosario for CS143!

From what I can tell from previous reviews, RRR is definitely a changed man. Lectures were occasionally amusing with some jokes here and there. However, lectures are also like a firehose of information with some lectures having over 80 slides. However again, lectures are recorded and I found going through the recordings to be really helpful (had to spend like 3-4 hours for a 2 hour lecture though :/). Homework was alright, but ofc it's always better to start early, but he allows 2 late days for an assignment (6 late days total) and since there are only like 7 assignments and 5 that are seriously graded the late days are actually pretty generous. Tests are hard, but they were open note so take good notes and index them or get an iPad and it should be alright.

I can't speak for previous quarters, but for spring online remote instruction he was one of my most considerate professors when it came to students needs. There were a couple of homework assignments (no projects) but none were particularly time consuming and he was quick to clarify and answer questions. It also seems he downsized the number of slides from previous quarters, so referencing the slides/handouts made the questions pretty direct. I felt that attending lecture (or watching lecture recordings) was still essential as he more clearly explains and annotates the slides in class. The final was a whole lot longer than the midterm but he went over what topics would appear on it so I didn't find any questions to be unfair.

Despite expecting a bad experience from all the previous reviews, I think Rosario took a lot of the student complaints from previous quarters and made a bunch of improvements and it shows. Overall, I feel like I learned a lot and was able to enjoy his class without having to stress about my grade.

This professor definitely has changed from the previous quarters, I'm not feeling anything negative mentioned in the previous reviews in his class.

Very very helpful class and material. CS143 + CS144 pretty much covers the basics for full stack software engineering. The biggest pro of Rosario's classes is that it is packed with information, so you can learn a lot from him. He is able to convey his ideas clearly, but I think one potential problem is that some examples in his slides could cause confusion for a beginner, but he might not be aware of it (as someone who already understands the knowledge). This requires a little more effort from you to understand and do some minor research, but I would say it's definitely worth it considering the amount of knowledge you will gain.
Regarding previous comments, I agree that Rosario has a problematic personality. In particular, his biggest problem is his pride / ego; apart from that, he appears to be mostly rational. Nevertheless, I don't see why this should affect the rating of his course. His primary job as a professor is to pass on the knowledge, and the primary job of me as a student is to receive this knowledge; and I think he has done a well-above-average job in doing so. In terms of personality, Rosario has his own journey that he should work on, so is everyone. I don't see why we should be concerned for him.

Just a warning this is the professor you are taking this class with:
https://www.reddit.com/r/ucla/comments/1ci3cl8/cs144_campuswire/

Honestly I do not know why Prof Rosario has such bad reviews. I will say that at times his lectures were a bit unclear (specifically a few topics like B+ trees) and he uses very specific phrasing/wording sometimes that you must know or else you could lose credit but his slides are helpful/easy to read. His class is recorded and you can reference the slides as well. For a CS class, I felt the homework was light and helped you prepare for exams. The coding projects were quite enjoyable in my opinion and not overwhelming. The exams were extremely challenging (the first one was okay but the grading was a bit brutal (i.e. very little partial credit) and the second one was probably the hardest exam I have ever taken and was super long), but the curve was so generous that it didn't matter. I performed below average on both exams (and failed both), did well on homework, and ended up with an A- so the curving must have been very generous. Rosario has even mentioned that you would have to try to fail his class, so at the very least if you put forth effort, you will pass the class. I think you learn very useful/applicable knowledge in this class and the lectures were fairly interesting to me and he would add in a joke here and there which was nice. I didn't do the readings and he doesn't require attendance. He is also friendly if you go to his office hours. I would take this class again!

This professor was great this quarter. I came into this class just hoping to learn SQL, but ended up learning a lot about a lot of different databases in a good amount of detail.
He isn't condescending or rude in the slightest, patiently answers everyones questions (though he does ask people to see him after class if the class is being held up too much) and is honestly kind of funny.
The projects were also well designed and extremely reasonable. Overall, I definitely recommend this class.

Now that the final lecture is done, I just want to tell everyone that Rosario is amazing and you really really shouldn't be afraid of the old reviews.

There's a highly vocal group of anonymous students here who are downvoting any sort of positive feedback because they are upset about the difficulty of the final and/or their grade in the course. Notice that most of the negative reviews were written June 20-23ish, 2019, which is around the time that final exam grades and letter grades for the class were released. Don't always trust the upvotes/downvotes on each review. I'll offer a change by focusing on positive aspects, which is something I believe everyone should do rather than unleashing their hate just because they have a platform that makes them anonymous.
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First, our Piazza forum had almost 900 posts, but the professor basically answered all of them. Yup, some students received unenlightening replies or were instructed to go to office hours when they asked about things that were discussed repeatedly in lecture, but most students who politely asked reasonable questions got helpful answers -- within MINUTES -- from the professor himself. If a professor did not care about his students, would he answer practically all of the students' concerns within 1-10 minutes when he could just assign the task to the TAs like other "oh so caring" or in other words "gives lots of A's" professors do? Do other professors stay up until midnight the day before the 8am final exam to answer all last-minute questions from students, like this professor does?
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Second, the professor is actually really nice and friendly in person. During the break and after class, I've seen students approach him and ask a few questions, and the professor would typically respond with a friendly smile and often laugh lightheartedly. If good questions came up during the break, he would announce them and clarify things to the entire class as soon as the class resumed. He also held extra office hours during Weeks 2-10 upon requests from students, and he held extra office hours during Finals Week that spanned several hours as well.
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Third, his projects were pretty interesting and sometimes fun although they were difficult. They were much more practical than other professors' projects, some of which were last updated a decade ago. He also gave extra credit on the projects, and they weren't too difficult as long as you planned ahead.
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Fourth, the professor is truly loyal to UCLA and gave several inspirational pep talks throughout the quarter. He mentioned how he did horribly in some classes here at UCLA but that it did not affect his professional career. He name-dropped several prestigious jobs he held and companies he worked for in the past to illustrate that grades don't dictate our future.
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All of my friends like this professor, and so does a good chunk of the class, which is evident because a lot of students continued to go to lecture even though it was at 8am. Students often laughed at the professor's memes and jokes, and generally had feel-good vibes as the class came to a close. We applauded the professor not once but twice at the end of the last lecture to express our appreciation. The emotional, vocal minority here on Bruinwalk does not reflect all 200+ students in the class. However, I do understand these students' struggles because this class definitely pushed us hard in terms of assignment workload, exam difficulty, and denseness of class material. Let's just remember to be nice to others even when we're anonymous so that we can collectively strengthen our community, do good things out there, and be regarded with greater respect from those outside the Bruin family.