What turns me off about DF?
Let's divide this into two categories:
1) What got in the way of the fun when I was starting out
2) What gets in the way of the fun now.
What got in the way of the fun when I was starting out?
1. Interface. How visually crude (and ugly, and distorted) the curses-style ascii was, how many menus, commands, and keys I had to learn all at once to operate a beginner fort, and how tedious it quickly got to manage dwarves. See addendum at bottom of post.
2. Lack of information. Utterly inadequate and cumbersome in-game manual. Failure to warn about even obvious perils (like a flood, an approaching lion, a trapped dwarf, or a lack of food or drink). No tips on what any room does, how to set up workshops and establish material production chains. No interface or basic gameplay tutorial.
3. Complexity of making even very basic things happen, or be done semi-effectively. In order to get logs, you need a dwarf with the woodcutting labor activated, an available battleaxe, and designated trees. You must be careful about how you designate; your woodchopper might start with the ones furthest away or begin work right next to a magma pit. The battleaxe might not be available; good luck finding it if you haven't learnt how to take an inventory. Thw dwarf might not be doing the work; you'll need to check paths and see whether other assigned jobs are constantly distracting the little dude.
What gets in the way of the fun now?
1. Sites where you can't experience much of the game coolness; the difficulty of finding a site with enough features to have fun in. Sites without adequate fuel and no way to get it, without wood, without metal, without sand, without flux, without fresh water, without interesting wildlife or inhabitants, without civilizations to interact with. The continued inability of trade to get you things you need in bulk.
2. The lag monster. Every fortress I've ever gotten serious about has died to the lag monster. The more coolness I reach for, the sooner the game bogs down in growing frustration.
3. Lack of underground interest. So many of the neat things in the 2D version are gone. Seasonal floods. Gremlins nipping for your levers, antmen coming out of your wells, batmen raiding out of a chasm you had to cross instead of one you can simply tunnel around. Adamantine you really had to work hard and face terrible danger to get at. At present, you don't even know whether you can grow tower-caps or find underground plants. Also, boring rock formations, metal-poor environments, and entire screens where there's literally nothing there except ryolite and microcline.
Addendum: copy of my first post on these forums (August, 2007)
Inconsistent keybindings. I trip up over and over again when trying to navigate the menus; no sooner than my fingers get the idea that 9328 navigates than they must re-learn /*-+. No sooner than I get used to the 'd'esignate interface ('d' to mine, return to select a corner, navigate, and return again to select a box) then I must re-learn how to plot a field or bridge (use letters). Some interfaces actually combine these. It almost seems the game is determined to experiment with every single method of using the keyboard to control stuff; this drives me to distraction!
Excessive number of commands. It is unnecessary to require the player to use 'q', 't', 'v', and 'k'; these should be reduced to at most three: one to look at a grid, one to look at/manipulate stuff, and one to examine creatures. Better might be using shift and control (look, examine, manipulate). Certainly better would be single left click to select grid, left click again to get details, or right click to manipulate. And the other hand stays on the keyboard to navigate menus.
Excessive depth of menus. It is unnecessary to require five keystrokes to start editing a dwarf's profession; an example of an alternative method within the limited space is to list the major commands, and then lump everything else into a '*' option. So viewing a dwarf's opinions would require 'v', then '*', then "return". Better would be right-click, pick from list.
Utterly inadequate information display on dwarves (the subject of several player add-on programs such as [Dwarven Manager] that I find more and more necessary after the first year). Sorting for skills, for unhappiness, for lack of rooms, for lack of current employment, for married status - these are just some of what we need to fully wallow in the coolness of this underground version of The Sims.
Disorganized information display. For example, you cannot learn what your soldiers are up without delving into the 'v' interface, the 'm' interface, and the 'x' interface. Even if you run through all these, the game won't tell you if a soldier knows where his barracks are, where his bed is, whether he recognizes a place to shoot or spar, or whether he really is actively using a quiver, backpack, etc.