In more development terms, to me, "incredibly hard" is embedded assembly programming (im probably not even using the right term for this) ...
The level of hard i would put DF at is "learning VIM"... which I think is apt, because 1) its a steep but rather short learning curve to get around, 2) over a while you naturally get better at navigating/commanding/etc and 3) there are plugins and "distributions" just like vim, to make it easier for a beginner, etc.
Now that I write this out, im thinking VIM is the perfect analog for DF :)
[NOTE] I'm a DF n00b. I have less than 5 hours playing. I'd say it took me about 30 minutes to "get it" though, and now I'm actually playing what I would consider "normally"