Outside of academics, UCI's biggest strong point, particularly in busy southern California, is the beauty of Aldrich Park, which is in the center of campus. There are lots of trees and paths, creating a nice setting for walking across to your next class or for just spending time outside.
Because of the large student body, it is difficult to get personalized attention for general administrative matters. However, some organizations like the Career Center, Counseling Center, Health Education do cater to students, which is nice. If you're a part of Campuswide Honors Program, it's really easy to get to know the staff, and they are VERY responsive to your needs.
UCI is definitely a large public university, which is great in the huge diversity in academic offerings and student organizations. Along with that, though, come long waits in line for administrative things and anonymity, which can be good or bad.
Most people do not know UCI outside of California. I generally say that I went to school in southern California or Orange County to not confuse them. In Cali, though, I think most people are familiar, but they think of UCLA or Berkeley first as their favorite UC.
I was really fortunate to have awesome roommates and to have on-campus housing the whole time I was at UCI, so usually if I wasn't in class or something, I would be in my dorm or apartment complex. However, the student center, eating places, and the library were pretty popular during lunch.
Although the school is UC Irvine, it's actually on the edge of the city and is practically in Newport Beach. Irvine is an upper-middle-class planned community, and Newport Beach is a pretty ritzy beach city. As a result, UCI doesn't really have a nearby ghetto area, and there isn't as much interaction with these areas as there could be with the exception of some pretty large donations from the rich businesspeople who live in the area.
Some people are extremely involved in student government, but from the outsiders' perspective, it mainly benefits those who run it (e. g. boosting the resume or lavish spending for their personal use), especially since many of them are also involved in Greek life.
UCI has no football team. Instead, we have a strong baseball team and a really nice science library. As a biology major who studied a lot, I had no problem with that, but it does kind of bring down school spirit as a whole. However, there is the enthusiastic Completely Insane Anteaters (CIA) organization that encourages people to go out to basketball games and such. Nevertheless, zot zot!
Probably one of my most unique UCI experiences was participating in Alternative Spring Break where a group of us went to a new location to do community service over spring break. I met such a great, diverse group of people and accomplished a lot while having fun too. Since I've gone, the program has done even bigger and better things, including restoring an area in the South affected by Hurricane Katrina.
As for complaints, everything is expensive: cost of living, tuition, parking, books, etc. Administration can be a hassle too.