Gamespy has put up two articles on Hellgate: London: a preview, and an article on the technology behind the game. Here's a quote from the technology article:
But the results are outstanding. In Hellgate: London whole
cities or underground networks spontaneously appear, different every
time. Like a kid with LEGO blocks, the game engine places large
set-piece environments next to one another and connects them with any
manner of randomized streets or corridors. Whole tenement blocks of
buildings are strung together from base elements. Buildings can be
turned or rotated as needed, and tons of random debris can be scattered
on the roads to make every area a unique challenge. In the underground,
corridors twist and turn and dead-end, snaking all around on top of one
another. It's easy to get lost. Of course, it's also fun.
There have been a few FPS games that have attempted randomly generated levels, like Soldier of Fortune 2. It didn't really work there, but maybe this will be different...