The thing that bothered me in Factorio when I played it some time back was that once you hit the end of tech tree, which is pretty easy (or at least was back then), then there wasn't really anything else to do, nothing more for your highly tuned factories to produce. That said, I really liked the part of building your factories, I just would like to have more reason to keep on building. Maybe competitive multiplayer spices things up, but I don't feel like that is where "the scene" is.
- The "no crafting challenge" mod, where you can't build anything by hand, only in factories. You get a factory to start with in order to bootstrap. Playing in this mode actually taught me that I had been relying on hand crafting way more than I should have -- it turns out that automated crafting of a lot of the stuff you normally hand-craft can actually speed up the game a lot. (Incidentally, I tried to create a "no inventory challenge" mod, where you start with a mobile roboport train car and have to use robots to build everything, but I found the modding API wasn't quite powerful enough to make this work well. But it worked well enough to allow me to conclude that this would be a pretty interesting mode of play if it worked.)
- Use a mod that makes resources spawn further away, so you have to build more trains. Trains are like a game in themselves.
- I hear people talking about "bob's mod" a lot, which apparently adds a bunch of new resource types and things to build with them, basically multiplying the game complexity.
There's mods, like marathon, which add additional levels of complexity and make ordinary things more expensive so that it slows the game down some. There is a space-based end game that's planned by the developers. And there's upcoming achievements, like make <111 items by hand.
You can try to build a CPU and have your factory run programs? I bet there are a lot of tricky solutions to be used (I tried for a bit, but didn't explore very far)
