Ranked mostly by my playtime therein. Thanks, Steam stats!
10: Hearthstone

9: Disco Elysium

8: Total War: Warhammer series

7: Star Traders: Frontiers

6: Hearts of Iron series

5: XCom 2

4: Kerbal Space Program

3: Final Fantasy XIV Online

2: Stellaris

1: Europa Universalis IV

If games out before 2010 were included, Lord of the Rings Online would rank highly (it’s become my default dork-around-aimlessly MMO just from the sheer amount of high-quality tourism and is more solo-oriented – at least for me – than FF14) as would Sword of the Stars 1, which was my go-to paint the space map my color game before Stellaris replaced it.