The problem with DF is that the UI runs off in a completely different direction. Playing the game requires untangling a mess of counter-intuitive mental contexts, using controls that seem to make little sense. It is an experience wildly different than the way one expects-slash-wants UI to behave. Artistically, one might say that DF's creators are making a statement against modern UI and its inherent complexity, but then I think that falls flat when you realize that the alternative (as in, what is it right now) requires considerable study to enjoy.
Is it artistic statement, or laziness? Or something else? Software, like all interactive mediums, has a functional component that you can't just ignore. If this were a painting, or a sculpture, or music, and I could only interact with it through perception, then that's fine -- entire art movements are built from challenging prevailing norms. But software is experienced through use, and no artist is immune to the practical considerations of their medium; rules which are best heeded. (Or not, but very veeery carefully and with great discipline.)
DF is a game, and games are meant to be played. This is a fundamental tenet of games. Play happens through approachability, among other things, and approachability is the product of an equation that includes good interface design. A game seemingly opposed to even a modicum of approachable design (something as simple as remapping mouse and keyboard controls to behave intuitively, as one would expect an ncurses-type app to act) runs opposed to very fundamental notions of game design. It is also terribly ironic, I think, and irony really is one of the basest and most-overused cliches in modern art.
Again, even the barest of olive branches extended to the community -- a simple, low-level API to hook into, or better default mapping of controls, or a recanting of their weird ideas of how windows should work -- would satiate this critic, as I really do want to enjoy DF. It is a shame that such brilliance is locked away in such a homely and unapproachable exterior.