I've played a lot of Rimworld over the months/years. It's great stuff, and there is a lot of content now. The modding community was big, too, and with the Steam release it's only gotten bigger. Right now I don't use any mods, as I'm still enjoying all the new content contained in the latest patches, but in the past I've added various factions and weapons.
It's basically a base-building/survival game with a little bit of trade and diplomacy. You try to create a self-sustaining settlement that can survive any number of ridiculous events. There's an ironman mode now, too, which is fantastic. It forces you to live with disasters, and there's actually a lot of things that you can come back from.
Combat is good in Rimworld, too. It's very intense, involves lots of tactics, and is a real challenge. I remember one battle where wandering mechanoids effectively closed off the east side of my base; most of my guys were wounded or dead from other disasters, so it seemed like it was the end. I had access to a building with a wall that faced them, though, so I got inside and built a whole bunch of turrets. Then I knocked down the wall to let the turrets engage the mechanoids, and used my other settler to flank and throw EMP grenades.
There's a constant sense of development and adaptation as the settlement grows. You can't rest on your laurels, or the events will fuck you hard. For example, I like to build early stuff with wood. Unless I remember to replace my old buildings with stone or metal structures, I invariably wind up seeing my base go up in flames. There's some fire-fighting tools you can develop and use, too, if you want to try solving the problem that way.
There's an endgame, too, if you want to call it quits. Just build a spaceship and blast off. Good luck if you're using the new game-mode where you start with 5 tribesmen who are yet to discover electricity.