If your gear is of reasonable standard you should be able to get through the post Praetorium storyline up to the current 2.51 story in a couple of days (and that's playing somewhat causally). The part that usually caught players out early on was in the 2.1 'A Realm Awoken' story where the player is forced to undertake the first five or so Guildhests as part of the main scenario (Guildhests previously being content most players ignored), and, after that, the player is then sent to undertake the previously optional dungeon Sunken Temple of Qarn (a level 30ish dungeon).

Other than that, it's pretty straightforward, consisting mostly of cutscenes and the occasional solo fight, with at least a new Primal fight towards the end of each patch story, plus a couple of new dungeons as well (Snowcloak and Keeper of the Lake).