It's a turn-based strategy game, so fundamentally it plays a lot different from Sins. You'll get the long-term "manage an empire" vibe that you get from Civilization or Master of Orion, in a good way.
As far as game design goes, Endless Space is very polished. There aren't any extraneous elements, or useless techs. Some of the late-game strategies, such as mass terraforming, can yield some enormous benefits if you're willing to invest. Unlike other 4X games, combat and conquest bonuses are useful throughout, and not swiftly outdone by industry and science bonuses. Watch out for the Cravers.
What can't be understated is the interface. It's sleek, smooth, fast, and intuitive. The interface contributes greatly to making the game a pleasure to play.