I've played it for many hours, and the thing that still asthonishes me the most is how incredibly efficient the code must be. While I haven't played with that specific purpose in mind, I've never managed to create a factory big enough where you'd notice a slowdown in the simulation.

Thousands of grabbers, trains, drones, belts, factories, aliens, environmental effects, different sorts of networks, all with their own logic, and somehow this game simulates it all like it's nothing. And it never crashed on me. You can make amazingly intricate factories all you want, but the truly great piece of engineering will always be the code that runs it all.