The World of Warcraft website offers version 5.2 patch notes, saying the Thunder King is now live in Blizzard's MMORPG. This post rounds up a bunch of Blizzard's articles with all you need to know about the new version, and here's the overview:

Patch 5.2: The Thunder King is now live! Lei Shen has consolidated his power on the Isle of Thunder, and if he’s not dislodged, his reborn army will threaten all of Pandaria. But the return of the Thunder King is good news for you, because it means that new challenges and triumphs await in our latest major content update. A massive new zone, a new raid, server-wide events surrounding the siege on the Isle of Thunder, new factions, world bosses . . . and more. Brace yourself for the storm.