Factorio was a pretty good early access success story as well. They were developing for a long time before full release and had lots of time to polish it. I think it helped that it was the kind of game that the devs could keep playing a lot without getting tired of it, and so they had a lot of opportunity to iterate on the design as they went. I think it's also the kind of game where good quality code has a lot of benefits for the game itself, given the scale of what they want players to be able to build and the need for reliable simulation for multiplayer. They also had a good principle of developing the core game design as a 'mod' itself, which made the modding interface pretty powerful.