ArenaNet's game designer Ben Miller has an interview up at Gamespot. Sporting several new screenshots for the upcoming expansion, Miller says:
: What can you tell us about the story and setting?
BM: The setting takes place in four major areas that sweep across the original map of Prophecies as well as to previously unexplored areas in the North. For the first time ever, players will get to see the Charr homeland, which is a beautiful, verdant land similar to what they experienced with pre-Searing Ascalon. The Far Shiverpeaks is home to the independent, Viking-like Norn. Everything about the Norn is huge and epic. Players will journey to an area of the southern Maguuma jungle known as the Tarnished Coast, where the magical Asura are coming above ground for the first time in centuries. Finally, players get to delve into the depths of the world itself and explore multilayered dungeons.
The story actually comprises several arcs that can be done at the players own pace and that tie into a much larger overarching narrative. Without giving too much away, I can outline the premise: Violent earthquakes have been shaking the world. This has opened up entrances into previously unexplored underground areas. Being the intrepid hero, the player explores them and gets swept away as a new peril stirs deep below. There are terrible mindless creatures that must be stopped at all costs. Along the way, we will be tying up loose ends with all sorts of previous characters, as well as foreshadowing the events that will set up Guild Wars 2. In many ways this is a prologue to Guild Wars 2. In general, players can look forward to fully voiced cinematics and an engaging, character-driven narrative.