Origins was the story of how you saved the world from *insert generic threat here*. They called it the Blight, but it might as well have been the orcs from Lord of the Rings. It was the same plot as every fantasy epic, ever.
While II was certainly less "epic", in that you were only really influencing the fate of a single city, it was at least something different.
But, to bring it back to the topic at hand, I figure III will be a medium between these extremes. The title, "inquisition", implies it won't be about stopping some otherworldly, all-encompassing threat, but rather resolving some nation-wide issue about mages that has been a major theme for both games.