OpenTTD is pretty cool if one likes slow Sim City like builder, and train logistics. Very nerdy but a serious game.
Discussion
Fun fact - back in the day I did graphics for OpenTTD. Especially things like icons... each pixel was selected manually in the yellow cursor 😁
Super cool! Thank you for your service! Although it isn't a game for everyone, due to complexity, I always found it to be a particularly beautifully crafted game :)