I found professors to be generally accessible when their office hours weren’t directly after their class. I was often the only student at office hours and generally had the professors to myself for one to two hours. I also had no issues discussing what I wanted to in class. But larger class sizes (40 - 80 students) might intimidate certain students from speaking up. UCLA was fine for me, and I got what I wanted from it. But this obviously isn’t the case for everyone. You have to assess your own needs and see if UCLA satisfies them.
I would say that most of my classes had a very clear structure. You can have a class with a great structure that’s still really hard for you though. Many science students, especially internationals, struggle with the writing requirements at UCLA, which are quite rigorous and uncompromising. I struggled a lot with classes in my own major (philosophy.) But they were the most interesting to me, and I did the best in those classes academically. The departments are generally well ranked too (philosophy at UCLA is generally ranked top 10 and is arguably underrated.)