Cataclysm was a good expansion for lore development. There were several new tools brought in to help the merger of gameplay and lore. There were just as many old tools that were reworked and reimagined in a way that made the story behind the game a fluid and interactive experience. And I'm not just talking about game mechanics like phasing and new quest technology; I'm also referring to the larger presence of novels and short stories that tie directly in with the game universe.
This isn't to say that Cataclysm's story was perfect. In fact, despite these innovations, there were problems abound with Cataclysm's storytelling methods. Zones played as seamless stories, but to many players, they felt as if they were on rails. Worse still was the lack of cohesion. The main storyline of Cataclysm felt to many just as scattered as the new zones we had to explore and level through. While Cataclysm was full of innovation, it seemed as though that very innovation led to an experience that ultimately wasn't as satisfactory from a story standpoint.
Mists of Pandaria is a stark contrast to Cataclysm. To be perfectly honest, it's a stark contrast to any WoW expansion we've seen to date. Throw your preconceptions of a world on rails out the window, because we're about to make the leap into dynamic storytelling.