Factorio is one of those sandbox games that keeps you hooked for hours. At first glance, I was quite sceptical about it. "Another one of those lacklustre sandbox games".
I don't know what convinced me to give it a try, but I ended up buying it on Steam. I played it for 1 hour. Soon that hour turned into 3. And that soon into 6. I've gotten so addicted to the "endlessness" of the game that I almost couldn't stop playing. I kept learning and finding new and effective ways to do things that I thought I already knew how. The more I play Factorio, the more I want to play. It just has this addictive aura, and I love it.
Efficiency is everything in this game. There's always a way to make your factories more effective and efficient. It's up to you to figure out how.