[Update]: After nearly a decade in development, Factorio has now finally been released!
After a rather lengthy development process, the simple yet incredibly complex factory building and management sim Factorio is just about ready to launch. Once the upcoming Version 0.17 becomes stable and polished, Factorio will finally step out of Early Access and launch as a fully finished game.
There is currently no exact release date set, for obvious reasons, but what I can tell you is that after April 16th Factorio's price will be increased to 30 USD (or your regional equivalent). So if you ever wanted to give Factorio a try, or at least do a bit more research about it, now would be the time to do so as you can still grab it for a completely reasonable $20/€20.
Before you make any decision, however, I would highly recommend you go and check out the most recent free demo. As you might expect, the demo only features a very small portion of Factorio, but it'll still give you an decent idea of whether its somewhat complex gameplay is something you're into or not. You can also learn more by heading over to either the official website or Steam.
And just for good measure, allow me to leave you with a gameplay trailer. It's a little bit outdated, but it should still get the point across. Enjoy!