Though it's obviously a sequel of the first Endless Space, it takes a lot of things from Endless Legend -such as Influence, the Marketplace, Minor factions, a Faction quest that permeates most of the game- with several new things to separate it from both Gone are EL's Empire plans, instead you have elections every twenty turns between six competing ideologies that determine which laws you can pass for bonuses at an influence per turn cost.
Not a direct sequel, it's more of an alternate retelling of ES1, with some new factions and a metaplot involving the Academy, the mysterious place where all Heroes go to learn how to channel Dust, and the ultimate goals of it's founder. Endless Space 2 is the latest 4X game by Aplitude, makers of Endless Space, Endless Legend, and Dungeon of the Endless.