Df is just like OpenTTD. Both are like Chess, easy to start, fun to play casually but it takes years to master. Great games, complex if you want to and a time sink if you don't keep an eye on it. Have had many hundreds of fun hours in both games
Dwarf Fortress is something like vim, where usually on the first interaction people don't even know how to start the game, let alone do anything in it.
Chess is easy to start, the rules fit on a post it note basically. Dwarf Fortress is difficult to start, and even more difficult to master.
Next week was spent on trying to survive the first winter...
As a 15 years vim user though - vim has a much more gradual but also much higher learning curve, I'm still learning new tricks in vim on a weekly basis.
Vim is mainly difficult to get into because the model itself is so different from what people are used to and there's inherent complexity. But, quirks aside, it's mostly very consistent and learning a few patterns will get you very far.
In Dwarf Fortress you need to fight not only incredible complexity, but also so very much bad UI/UX and inconsistencies between what should have been identical actions. A great example is searching a list of items. This is done with q for query. Or sometimes s for search. And in some cases f for filter. Or even better, the way k, v, t, q, are all just needles variants of "look at thing under cursor". And none of them work for some activity zones such as pastures, then you need i.
As much as I love DF I'm very much looking forward to the Steam version, mainly for the UI overhaul, which is so far looking really promising.
I'm hopeful that the upcoming Kitfox Games version makes it very accessible to lots more people.