It's like Space Hulk?
A villain from previous Operations returns with the Dread Masters, six Sith Lords who mastered Battle Meditation. It brings this, plus the Gree species, all together into a horror-themed Operation dealing with the mysterious Hypergate and the Terrors from Beyond it holds. The developers talk more about the encounters, the story and the treats they have in store. Be warned though - if you wanted to go into it blind, spoilers abound.
And, in case you want to take a shot at 1.4 before it's live, it's up on the Public Test Realm.
Julian "Mirai" Williams