Basically this DLC is a must-buy for Stellaris. It adds basic elements of gameplay that improves the player's experience by various ways, since adding the Ascension paths that I can't imagine myself playing without them today, and adding the Dyson Sphere and Habitats that are huge improvements to the early and mid game. Basically this dlc adds a lot of flavor and elements for the game that you can't play without them once you get a taste. It should be part of the base game.