A great modern version of Transport Tycoon, one of the defining games of my childhood. While this doesn't have the charm of the ancestor, it's still a really well made and great-looking game with a little cumbersome UI.
The campaign is really good, leading you through 150 years of transportation history in a light-hearted but fairly accurate manner with a surprisingly excellent soundtrack!
It's still getting updates and has many workshop items and mods.