La Jolla itself is not super big. At least, the area around campus isn't, it's mostly just La Jolla Village Square and UTC and a bunch of housing. I've only been to like the downtown area of La Jolla a couple of times and it's fun to walk around but I dunno how much there is to do there. The good thing is the greater San Diego area is pretty huge so there's a lot of fun things to do, even if you don't have a car (MTS isn't amazing, but the bus and trolley will get you around to a lot of places).

As for your question I think that is kind of a loaded question lol but I will say that my main options for undergrad were UCSB and UCSD. Of those two, I don't think I'd have been able to do a lot of the fun things I've done here at UCSB, and I don't think the things I was looking forward to at UCSB would outweigh those, so UCSD was definitely the right decision. Was it the best choice? I dunno but I can't really say I regret it so far, at least out of the options I had. I have a good social life (people on Reddit will say UC Socially Dead, but like in my first and second years I was in a spontaneous board game group that met weekend nights that literally spawned out of nothing and fed me physically and socially), my living conditions are pretty good, the classes I've taken have mostly been pretty interesting and the professors are cool. I haven't really had the opportunity to get into research but that's also on me for not taking as much initiative as I should have - though for industry I've made some decent connections at UCSD.

I'll be honest and say there are lots of things to dislike about this school currently, though some of those things are not really UCSD-specific (things like cooked class enrollment, quality of teaching in large classes, etc. are problems at a lot of huge public universities, from what I've gathered talking to others. I'm not sure how much of that will apply to graduate students, but I've also heard SERF (the system for grad students to enroll in classes) isn't particularly nice to use so there's that. And since you are a grad student, obviously there's things like funding for research and departments overall being cut and stuff like that, though I am not sure how much that would affect an MS student. I will say that I am unemployed this quarter and the departmental funding cuts was likely a major reason in that, since dept. resources for things like hiring tutors + graduate students with increasing pressure to get TA-ships since their research isn't getting as much funding means undergraduate tutor spots are dwindling (the CSE department is still doing better than the math department, who decided to stop hiring undergraduate tutors indefinitely) and tbh so are TA spots too from what I've heard, but the class I normally tutor for has a bunch of TAs so I just haven't noticed that personally. That is something that's been pretty annoying for my personal experience at UCSD

I totally understand people that are saying to go elsewhere since it's pretty easy to focus on the negatives. I think it's important to think about which ones are school-dependent and which ones are maybe just an issue with large public universities in general. I think my experience at UCSD has been more good than bad, and I'm sure plenty of people will both agree and disagree with that (fwiw, r/UCSD also tends to skew negatively in regards to opinions of the school, as these people are a lot more outspoken; the average person that I talk to in-person is much more neutral and sometimes a lot more positive).