Before I attempt to justify yet another suggestion for making Dwarf Fortress more playable, I want to thank Toady One for making it in the first place. Let's face it: we all love Dwarf Fortress as it stands, because... well, I won't get into the !!list!!, or we'll be here all night, but let's just say there is a !!list!!. That said, on to suggestion...
There are a lot of discussions out here about overhauling the user interface to make Dwarf Fortress easier to play. I'm going to come out with what seems to be a rather unpopular and undervoiced opinion and say that for the most part that's unnecessary. The one thing Dwarf Fortress's (fortress mode*) user interface needs requires no major overhaul (from a high-level design standpoint anyway) and would not be broken by later changes to gameplay features -- and therefore theoretically could be added without waiting on anything else. (Furthermore, I haven't seen it suggested -- though it's quite possible I've merely missed it, sorry if I have.) For these reasons I believe it deserves its own thread rather than merely to be added to one of the dozen supposedly complete and unified lists of user interface transmogrifications. Ready?
I think most user interface overhaul ideas address the complexity of Dwarf Fortress's menus. However, the complexity of the menus largely reflects the complex variety of tasks you can perform in Dwarf Fortress; there's not a lot that can be done to reduce it without taking away from gameplay options. (Some of it could probably be better organized, such as having one place to view multiple dwarves' labors like Therapist in-game, but that's another story; indeed, some screens have only gotten more complex when overhauled in the past, such as the military, so we should be careful what we ask for...) More importantly, it's not complexity that's the issue; think of other games you've played that you could at least get the hang of the basics without a manual or guide: the ideal game, without forcing you through a tutorial or holding your hand through the plot (which is the even more annoying opposite extreme), gives you enough pointers in the beginning as to how the controls work and what your options are that you can pick it up while playing it. Dwarf Fortress is hard to learn not so much because the menu is complex as because the menu doesn't explain its own options.
For instance, as a new player a couple years ago, the options "mine" and "channel" didn't tell me the difference between mining and channelling. It took me longer than it should have to figure out why "build->construction" and "designate" seem to have many of the same options and what the difference is between these two versions of them. Selecting "build->chair" told me I need a chair first (which came first, the chicken or... the chicken?), which left me confused as to what building one is if it doesn't make one (and the same issue exists for all furniture). I didn't even realize at first that stairs connect Z-levels straight up and down in the same spot (as opposed to the sort of diagonal traversal they occupy in my real-life house). There are probably more examples, but these are the ones that I recall from my own learning experience.
Now, all of these confusions could be resolved with very brief descriptions of different menus and menu options (these are just example proposals to show how it could help):
main menu, hidden: "(Press tab to show the menu.)"
main menu, shown: "Press the highlighted keys to access menu options."
designation->mine: "Dig out tiles on the current z-level, leaving the floor"
designation->channel: "Dig out the floor and the tile below, connecting them with a ramp"
designation->carve upward ramp: "Dig out the tile and the tile above, connecting them with a ramp"
designation: "Shape natural terrain or act on the environment"
build->construction: "Place materials as artificial terrain"
build: "Place furniture, workshops and other constructions"
build->chair: "Take a chair (created at a workshop) and put it somewhere to be used"
[build->construction/designate]->up stair: "Place/Carve out a stair connecting to matching stair on tile above"
[build->construction/designate]->down stair: "Place/Carve out a stair connecting to matching stair on tile below"
[build->construction/designate]->up-down stair: "Place/Carve out a stair connecting to matching stair on tile above & below"
Of course, we need somewhere to fit even brief descriptions. Well, there's really only one place available in DF's limited screen space. If announcements fit in the bar on the bottom of the screen, menu descriptions will have to fit in the bar on the top. Or vice versa -- I forget whether announcement position can be set in the init options currently, but an init option to swap announcement and menu description positions would probably be nice. (Even those examples might need to be trimmed a little to fit along with fps and idlers, unless they can switch back and forth between first and second halves of the message, but I suppose it'd be best to avoid that.) Don't forget an init option for experienced players to turn the descriptions off so they don't feel like a fairy is hovering in their face advising them, while we're at it.
The important thing to recognise here is that this relatively small addition is all it would take to make it possible to learn the essentials of Dwarf Fortress simply by browsing the menu and maybe experimenting a little. Or more to the point, experimentation would no longer require new players to deduce both the nature of the action and how it plays out, only the latter. Sure, we'd still need the wiki to look up which materials are magma-proof or to discuss complex mechanical strategies. Sure, we'd still post Let's Plays on YouTube just because we can. Sure, we'd still ask other players on the forums for advice on handling aquifers. But I think making the menu self-explanatory would go much farther than larger overhauls toward eliminating the problem where many people simply cannot learn to play Dwarf Fortress without somebody else walking them through it; and all that without any need to wait for the feature set to stabilize or the Year of the User Interface Overhaul to arrive, because all it takes is changing menus and their options from having a name alone to having a name and a description.
*Note: There's a fairly simple reason this suggestion is directed only at fortress mode. The help menu that lists actions and their keys in adventure mode gives actions larger, mostly self-explanatory names. Further sub-options in an action during play such as conversation choices or attack targets likewise either are described or are self-explanatory. In other words, adventure mode's design is already more or less equivalent to this suggestion.
Toady, if you're reading this, thanks again. Indeed, thank you to anyone who takes the time to read and consider this. Let me know if there's anything I didn't communicate well and could make clearer, or if anyone has any ideas how to improve on this notion.