Spoilers for every single Cataclysm raid and zone to be found here.
On the whole, Cataclysm has revealed a great deal of lore for the Warcraft universe. We've been to all four of the elemental planes and destabilized two of them by destroying the elemental lords who were effectively the dictatorial forces of their respective elementals. As of this writing, only Therazane remains as undisputed master of her elemental plane. (Indeed, with the destruction of Deathwing, she's actually in a stronger place than she was.) We've seen the Twilight's Hammer cult rise to world-shaking prominence and played a role in setting them back by destroying Cho'gall. We've finally managed to balk them on the eve of their Old God masters' final triumph by destroying Deathwing just as he was about to unleash an even more destructive assault on Azeroth than his first.
The Dragon Aspects lost their immortality just after we discovered that there were actually safeguards in place to appoint new ones. We discovered the secret land of Uldum and its Titanic ruins, and we prevented the activation of the Halls of Origination at Deathwing's behest and discovered the connection between the Qiraji and Uldum. We also saw the war between the Alliance and Horde begin lurching toward a new phase. We discovered the fate of Gilneas and the Gilneans, saw tantalizing hints as to the development of the goblin people and their mysterious kajamite, and even more. It's been an eventful expansion in terms of what it established. For the next couple of weeks, I'm going to talk about where Cataclysm took us and what we discovered.