Something Stellaris do unlike any other strategy game is the way it offers a universe full of undiscovered mysteries and exploration opportunities . It is not only those factions who lives in space. Seemingly neutral species and other phenomena flying through space independent of what you are doing, and through certain projects these can be researched and mapped. You may learn something new from these creatures that unlocks additional research opportunities .
One of the coolest things I came across was when I colonized a planet and found out that it was inhabited by Titans - enormous creatures a la Hercules and Greek mythology. I was stupid enough to think that everything would go well. In a short while the planet was taken over by the Titans , and wave on wave of expeditionary forces were not able to take it back. A sad end there then, but the discovery was no less spectacular for that reason.
Not only can you discover ancient mysteries or clues that will take you on all sorts of adventures, but you are lucky during exploring then you can come across intelligent creatures who are trying to evolve into an ordinary fractions. One of the most unforgettable I have done was to make an observation post of such a planet, that enabled me to pay attention to what these creatures where doing. Before I knew it I had kidnapped " copies " of this alien race . To my great surprise , this led to the nations on the planet gathered against me . It all ended in me , through advanced technology, infiltrated government on the planet , helped them with technological advances so that they became a full-fledged faction , and then I made them to my vassal . That is long term strategy like nothing else! However if you just want war action and controlling ships in combat this game is nothing for you. I can't wait to play this in multiplayer against some friends:)