I live in a hall of residence. It's not bad actually, very social, though the food stinks. Well, I can't speak for all halls, so I'll stick to mine. They can't be that different.
Commonwealth Hall is one of the larger intercollegiate halls of residence of the University of London, which accommodates 426 students on nine floors. It was built and opened in the 1960s, and as such exhibits some timeless architectural features of British public buildings of that time. Specifically, it's absolutely fugly, and from any angle, it looks like a square mass of battleship-grey concrete, with whitish concrete cladding and a spot of red-brick as an afterthought to make it look slightly less offensive. Other University of London halls that I've seen look rather similar to this, except different shapes.
The interior of the hall, however, depends on the floor on which you are. This is because the University doesn't have the budget, or more likely, doesn't want to spare the money, to renovate all the floors at once, so one floor is quickly re-done over the summer at a time. So when all the floors have been renovated, the first to be updated thus falls into disrepair. After all, students will be students. The other thing about the hall's interior is that it eerily resembles scenes from Kubrick's The Shining. Endless, claustrophobic corridors, all of which look the same. To the untrained eye, it very well could seem like a maze of twisty little passages, all alike. Especially as, contrary to what has been said above, the corridors are almost never renovated.
Now, halls of residence almost certainly have the best social life. You can only go so far sitting in a grubby flat with five other student bums like yourself sitting around drinking cheap beer and sharing a Camberwell Carrot and talking about things in increasingly slurred voices. In halls, you can do that anyhow, but with up to 426 or so different people. Furthermore, often halls have their own Junior Common Room, which organises social events such as Valentine's balls, excursions to clubs for random reasons, and whatnot. Although this varies from hall to hall.
Thus, in all, if you do want to go to a university in Great Britain, seriously consider getting into a hall of residence, at least for your first year. But make sure you have a look around first before deciding on one! The KCL hall of residence at Stamford Street has, apparently, staff who are very happy to fine people up to £50 for accidentally setting off the fire alarms, loitering in the courtyard, and similar. Be wary of things like that.