It's a 4X strategy in space. You rule an empire, which you get to customize: appearance/genetic origins (humanoid, plantoid, insectoid, something weird etc., as well as starting world status, which defines which worlds your people would find more hospitable for a while), traits (positive and negative — good for roleplay and trading for more powerful positive ones) and ethos (how your people see the world, themselves and others in it, what they derive happiness from, possibly their work ethics etc.).
You start on a single planet, and expand your reach through colonizing planets, diplomacy, cultural domination (I believe it's possible to "convert" other empires' planets to your own if you have them within your empire's territory for long enough) and/or scientific research. You get to further customize your empire by issuing edicts, each affecting one portion of your empire's activities — be it encouraging free thought, improving spaceship building speed or producing a higher number of resources — or changing its policies, like the empire's attitude towards AI, severity of planetary bombardment of its enemies' planets or the kind of slavery, if any, it has.
The game has a rich and slightly randomized scientific progression, in that you a choice from a limited randomly-selected available technologies after the previous one is researched, in each of three categories: Society (things that deal with population, ethics, policies etc.), Engineering (ship and building upgrades, as well as new ship modules) and Physics (new ways to abuse the laws of nature to your advantage — i.e., new types of weaponry and space drives, among other such things). Further research provides opportunities for new empire modifications, as well as potential risks some dangerous technologies provide, like AI rebellion from researching AI.
In space, you can deal with other spacefaring empires as well as pre-FTL (faster-than-light travel) species. The latter, you can observe, actively study and uplift; once they reach space, either on their own with time or by your hand, they may join you as an ally. You also get to deal with native space inhabitants, study anomalies (things of unique nature, which may yield positives, negatives or both — the result sometimes dependent on the choices you make within the anomaly mini-events) and take part in (or opt out of) storylines, quests and crises, each of which is unique, with some offering shallow but creative usage of sci-fi tropes.
It's a nifty little thing.