Leif Chappelle is on the content design team at ArenaNet and has a post on the official blog about the evolution of narrative in personal story:
To start with, let’s talk about the numbers involved. Each of our five playable races begins with its own starting area—this is where your story commences. You likely know about the biography in character creation, where choosing one of several options translates into a different story for your character. This three-way split exists for all five races. Furthermore, each of those three stories contains decisions you must make that further affect how the story plays out. This means that, to experience every potential storyline being told from level 1 to 10, you’d need to play the game 30 times (5 races times 3 initial stories times 2 internal branches in each storyline). And that’s just the first ten levels of the game. We have 80 levels of progression for your character, and every ten levels or so, you’ll begin a new chapter in your story. The game does not sputter out at the end, either, as you’ll be experiencing some of the most involved and epic story steps in the game with huge battles and fearsome bosses, but that’s a story for later.
It certainly means you won’t be presented with an insufficient number of ways to ensure that your personal story is different!
When you’re playing through the game, you’re going to see an amazing open world with plenty to do, but you also get to play through the equivalent of a full-fledged single-player RPG into which you can bring friends in order to experience it together. And the diversity of gameplay you experience in these storylines is truly varied. Whether you’re chasing a mystical creature through an undead-infested swamp, going undercover as a pirate and competing in a bawdy drinking contest, playing a bit of tower defense with turrets and troops against an onslaught of invading ghosts, sneaking through a city at night, or leading a huge army against an overwhelming foe, you’re going to find a lot to enjoy as you experience your character’s own personal story.
Read the whole thing at the ArenaNet blog.