Dwarf fortress is the first thing since MUDing that's really scratched the imagination itch in quite that way and, as someone who has worked in game development themselves, I think it's something that is only possible if you keep to the lowest tech. If you use words or abstract symbols then each player will fill in the details themselves, usually in their head but sometimes in artwork (see Kruggsmash as an approachable example here[1]) which can be extremely fulfilling.
I hope to see the non-ASCII version work as a gateway drug to get more people into the imagination of what they're building. And I hope this didn't come off as ranty or judgemental - each person enjoys games in different ways... but low detail art has a way of really spurring the imagination on!
So you begin to do other things, mega projects are a common one.
In one of the last times I played, some invader had broken through my defenses and killed a couple of highly respected dwarves (one of whom was a skilled fighter), but finally came face to face with a young girl dwarf who confronted him in one of the dining halls and, though she lost a leg, managed to kill him (eventually recovering to grow up to be a skilled craftsdwarf). I had a some statues made of her, and most of them came out depicting the heroic deed in different levels of detail (so of course the best one was put up in that dining hall).
There's also a sort-of-exploit related to this, where if there's a stranger in your fortress whom you suspect of having a nefarious background, you can commission artwork of them and sometimes it will reveal malicious traits about them if you examine it. The artists always seem to have perfect knowledge of their subjects.
ASCII version will get the new UI Soon™
Personally I don't think the new look they're going with will be problem with imagination for me - the new look adds just enough detail that you can spot dwarf by their look alone but there is still plenty of space to imagine how exactly the described things look
I call ONI my "dollhouse."
It's such a sleeper compared to similar games. The art and sound effects really elevate it. Klei has such a unique art style and it's really shown off. Also has a much more interesting "survival" curve than most; you'll be presented with many many hours of challenges trying to get a sustainable base, without cheap tricks like ever-escalating interruptions based on quantitative progress (looking at you, Rimworld.)
Most days I preferred ONI due having to go way out of your way to commit war crimes, whereas in Rimworld it's just clicking a couple buttons.