AOE2 (Age of Empires 2) is _still_ going strong some twenty years later. Active reddit, youtube, and twitch communities. Still releasing new civ expansions on Steam. I think it's success is due to just how balanced the game is. It's like a really fast moving chess game.
I like factorio as well, but honestly it started to feel like work after I got the hang of it (needing to refactor etc).
Played a lot of Age of Empires 2, fantastic game. Been spending more of my time playing 'Supreme Commander: Forged Alliance'[0]. It has a community lobby system over here[1] that's pretty active (over 1400 simultaneous players at time of speaking).
I got infuriated by some of Age of Empire 2s limitations (e.g. limited selection size, awful pathfinding, games tending to stalemate). The extra ~decade SupCom had seems to have helped.
The Steam version often goes on sale for a few dollars once a month or so[2].
I like factorio as well, but honestly it started to feel like work after I got the hang of it (needing to refactor etc).