I never lived in halls the second time I went to uni, and made lots of close friends. I think it's a bit of a myth that you need to live in halls to have a good social life. For some people, it does help, as it means they have some people to go to events with, and obviously if you have a good set of flatmates then you're hopefully going to have a good time. I've never really known anyone who didn't live in halls to feel like they were missing out a lot, and I think for some people who get on with their flatmates ok, it can actually be a bit limiting, because they don't put themselves out there to meet other people they might like even better.
I think the thing with housemates/flatmates is that you live with them 24/7, so if you don't get on with them, it's always going to be pretty awful. Actively falling out with someone who you still have to live with for the next six months (say) is never going to be ideal. Equally, living with someone with a very different lifestyle to you can be really hard.
So, I don't think living in halls is important, but I do think liking the people you are living with is- and I would say if anyone is having a bad time in halls they should ask to move ASAP.