One that you need to firmly keep on your watch list is Songs of Syx, a city-builder that starts off tiny and allows you to grow into something huge.
Written about here on GamingOnLinux back in July, with a tech demo available to mess around with available on itch.io. Shortly after writing that article, the developer actually put up a brand new demo with a ton of work going into it so it's worth taking another good look at. Not only that, they also now have a Steam store page for you to wishlist and follow along ready for the eventual Early Access release.
This certainly isn't your usual city-builder though! The developer has a clear vision for the game to include massive battles, trading, immigration systems, easy modding, a story mode, a seasons and weather system, a dynamic culture system and plenty more fun sounding features as the list just goes on for a while that should make it quite a big game.