But with Legion, Blizzard continues its streak of integrating the best of contemporary MMO mechanical design but also radically alters the balance of power in their world for the first time since 2010’s Cataclysm. It’s a gamble that pays off.

Legion finds Azeroth’s greatest existential threat making its first return since Burning Crusade. Thanks to the treacherous orc warlock Gul’dan (who lives again thanks to the events of Warlords of Draenor), the titular demonic Legion has been set loose on Azeroth once more. Although the Alliance and the Horde combine forces at the expansion’s beginning to turn back the tide of this invasion, their attempts are crushed. You are then tasked with finding the Pillars of Creation–ancient devices created by the Titans, who predate mortal life on Azeroth–which are the only hope of closing the portals to the Twisting Nether.

http://www.gamespot.com/reviews/world-of-warcraft-legion-review/1900-6416527/