The Cataclysm expansion set out to do what prior expansions tried to do, and improve upon it in a significant way -- significantly inject lore into gameplay. And to some degree it worked; players found themselves working their way through zones both new and old by taking part in an interactive story. In between, we had short stories and novels that tied directly into that gameplay, weaving each part of the Warcraft franchise together into a solid storytelling tool.
But it also had its flaws. Storytelling in zones was fantastic upon first playthrough, repetitive upon repeated play. The story of Cataclysm was so widespread that it didn't seem to have the kind of dramatic impact it was intended to have. And Cataclysm introduced so many loose threads of story that trying to pick a clear resolution out of the tale was difficult, to say the very least. And then we have the ending, signifying the dawning of the "Age of Mortals" with no clear definition as to what that really meant.
We've got a little more definition now, and it's from an incredibly unlikely source, the last part of the franchise that didn't seem to have any significant lore tie-ins at all: the WoW Trading Card Game.
Please note: Today's Know Your Lore contains some minor spoilers for Jaina Proudmoore: Tides of War. If you're looking to avoid all spoilers, you may want to come back when you're done with the book!