Vex, Atheon makes a come back due that time traveling stuff they do. Guardians start join in the dark or faction tensions rise, so powerful guardians become bosses. Cabal finally become relevant and a massive raid inside cabal territory. House of Kings grow since the others have taken a dive and you must defend the tower. And then there's the Traveler, you enter the Traveler and must fight your way through Vex to it's heart and destroy the deceptive entity. [spoiler]That last part only makes sense because it's rumored that the original story revolved around the Traveler secretly being evil and feeding off praise, so it made the Vex and the Darkness.[/spoiler]