Gurgh... I have to be one of those people that's listing a bunch of "it's not finished yet" games-for-geeks (probably) but here goes.
I'm a glutton for sims but the interface for DF makes we tear my hair off... nine times out of ten seige failures or tantrum-spirals are a direct result of me bollocksing something up in the interface. In terms of sheer unadulterated fun, Dwarf-Fortress-meets-Firefly-colony-sim
Rimworld is much less frustrating for me (but only 2D). At the heart it's a little basic but there are a bucketton of mods available for this and it's really come into its own in the last year.
In terms of "Oh my god I will be seeing conveyor belts in my sleep for the next month", factory simulator
Factorio. Combine with Bob's Mods to turn a fairly complicated puzzle game into a twisted journey through a bizarre periodic table.
But in terms of the sheer amount of time I've spent on it (I think it's eaten more time than
just one more turn in the Civs), if you like the build-your-own-battlefleet Lego-with-gatling-guns-for-people-who-like-building-self-replicating-balloon-assisted-AI-controlled-missile-platforms genre... there can only be one
From The Depths. Bit of a learning cliff to start off with given the occasional bind-moggling complexity of some of the components, but worth it when your jet-powered hydrofoil executes a perfect HMS-Victory-style manoeuvre and nails the enemy phalanx with a double broadside of sonar torpedoes.
