What's your favorite MMO dungeon?

I've been running a lot of flashpoint PUGs in Star Wars: The Old Republic lately, mainly because I'd like to finish my story quests but I can't bear to level via the usual FedEx-this-and-kill-that paradigm any longer. I've never been a dungeon crawler, but the SWTOR variants I've done thus far have been pretty enjoyable, mainly because of their nods to Star Wars lore.

What are some of the dungeons you've most enjoyed over the years? Did you enjoy them due to the mechanics, the story, or both? What's your favorite MMO dungeon?

TH

Definitely has to be Darkness Falls in Dark Age of Camelot.  It was a RvR (PvP) dungeon that was controlled by a realm, but the people who were in there when the control swapped hands aren't kicked, they have to be pushed back and wiped out by the attacking force.  Lots of fun.  Wulin assassins are pretty cool too, but not quite on the same level.