I found Broken Valley post fortress invasion to be really rather depressing. I remember going to look at Broken Valley Village, perhaps my favourite spot in the game, and feeling miserable that an enormous flying rock had landed on it. Killing every one of the baddies in the area didn't really help.
On the other hand, there was some nice loot to be had, as Raze says. Also interesting finding out the fate of the odd person if you explore enough. Actually there's just the one I can think of offhand but y'know.
