I think this is a tentative step into a storyline from Maxis as they are not quite sure if we will like it so it is bound to be a shorter adventure. Some of us Simmers don't play adventure type games usually so this is short storyline is just right for me.
The reason I got bored with Sims Medieval was because I had to go through that too long introductory tutorial before I even started the game proper and Maxis should bear that in mind with similar adventure type packs and allow us to bypass the storyline if we want without losing by it.