Stellaris is a huge game. Think Civilization fused with Sins of a Solar Empire, set in space with plenty to do and you essentially have Stellaris. Originally released in 2016, the game has been continuously updated with free patches and optional paid DLC, but if you've yet to try it out you can get the game right now with up to 75 percent off on GOG.
One of the best aspects of Stellaris is the early game, which make you feel as though you truly are exploring space for the first time. There are events that can occur, requiring you to make decisions, explore unknown territory, or embark on incredibly dangerous expeditions. It's space exploration at its best, albeit from a civilization management perspective.
The main game is available on GOG for $11 and you can pick up some of the DLC for less too, saving you 50 percent for each additional content package — a fine deal for such a grand experience.
