Pros
I can really only speak for the physics department (and my subfield specifically), I'm sure the experience differs for other students. UCLA physics seems to be a pretty good place to do graduate study. -The professors are top-notch researchers and I've found all the projects I've been involved in to be fairly interesting. -The other graduate students are hard-working and very smart. -The atmosphere is very academic, but also pretty laid back (I wear shorts and a t-shirt literally every day, and my hair/beard is crazy and no one has ever cared). -Lots of opportunities to network with big names in the field; professors are always arranging talks/conferences.
Cons
-Average time to PhD for theoretical physics here seems to be about 5-6 years. That's a long time, but it's also pretty average for the field, I'm told. -There is definitely a lack of women and POC in the department, but students/faculty are actively working to increase enrollment, and this is a problem in the field as a whole, not just at UCLA. -I wish I was paid some more for my TA duties, but I'm not living in poverty, so I guess I can't complain. -Be expected to work 40-60 hour weeks if you really want to get your work done (but hey, that's grad school!).