I've been at UEA for quite a few years.
There is not one particular thing about it which makes it stands out, except the fact, it is simply unique. I don't think there is another university which has such a close, sort-of family feel to it; from day one, you feel part of it.
A wide variety of opinion, background, profession, study, tastes and what not are found on and off campus; there is something for everyone. The schools are all very close to their students. There is not a corporate feel to the place (though I have found this to be changing a little in recent years) like many other universities. It is actually about education, and more importantly, enjoying it.
I should think one of the main reasons for this is its relative obscurity and georaphical isolation. The nearest university town is Cambridge (which is quite a way away), and being apart from the rest of the world gives it a genuine identity, and this feeling leads to a positive and happy lifestyle, as expressed in the National Student Survey. It doesn't need to be justified; it simply is the coolest place to be.