Well, when I first came in, looking at ASCII was like looking at the Matrix. Experience has changed that, of course, so now I see elephants attacking a human that dropped his weapon instead of EUE/
I never had too big of an issue with the interface, tbqh. The wiki tutorial helped immensely, though, so that negated things. An in game tutorial map would be great, though. :I
I'd say the thing that irks me most is the lack of realistic economics, which I know will be coming in the caravan arc, but still irks me. Just because I think DF would be a totally awesome economic simulator. And without good economics, there isn't much incentive to do anything, really, except get bigger and bigger numbers in 'created wealth' during late game. Proper economics would both add meaning to a fortress (being able to specialize your fortress and have the world respond accordingly) and could also reduce micromanagement (by having rich dwarves do things like hire out-of-work dwarves, or the out-of-work dwarves could start doing things on their own like painting, writing, or you could privatize a workshop and have them take orders from other dwarfs, stuff like that.)
And skill gains happen way, way too fast. Legendaries should be singular people that are on par with people like Michelangelo, glowing with talent. Not Urist McFishdissector who got reassigned to engraving last year.