The primary draw, for me, is the unique combat system. I find it inherently fun, somehow, for my RPG character to go for a disabling shot to my enemy's leg, disarm them with targeted shots to the grasping limbs, and then behead them or make them bleed out to cause death. That contrasts to most RPGs or RPG-like action games, where (in their purest form) it's just a matter of reducing an abstract HP value to zero. Of course, by itself, that wouldn't be enough to hold my interest in the long term, but the other aspects of adventure mode add just enough variation to keep me interested. Exploration, quests to kill various things, getting to experience the world's history, that sort of thing.
Now, I did feel that 0.31.25 adventure mode was a bit sparse, in terms of stuff to do. After the initial round of bandits, which tended to be fairly weak, I didn't have a lot to do other than trek to some fort, get a quest to kill a single massive beast a few days' travel away, rinse, and repeat. It didn't take too long before I started getting bored of the grind, even though I wanted to keep playing with the combat system. Luckily, Wanderer's Friend helped with that, because item forging (and in particular crafting decorations from dragons and such) is a valid long-term goal, however shallow it is.
In 0.34.xx, though, I find that there's a lot more to do, while I play with the combat system. Human enemies seem to be more plentiful and harder, particularly if I turn down the werebeast number; there's finally interesting loot that gets created in world gen; there are necromancer towers I can assault; I can become a vampire; completely wiping out a large city sounds like fun now, what with the keep in the center and the ability to stage a zombie apocalypse; etc., etc.. I've also started playing around with raw editing, and eventually want to make the random wild critters actually interesting to fight, which will also help break the monotony of traveling a few days away to kill a lone dragon.
I suspect that NW_Kohaku's issue with adventure mode, though, is that she (?) doesn't find the combat system to be inherently interesting, from the way she's talking about it. Which is perfectly fine! Not everyone finds the same things interesting in the same ways
. It sounds like NW_Kohaku is more interested in simulations, building things and deconstructing systems, right? So, for someone like that, fortress mode and modding definitely seem like they'd be more interesting than wandering around a shallow open-world RPG and finding different ways to kill things. I personally had a similar issue with Morrowind, when I finally got around to trying it. For some reason, I didn't find the combat or character development systems all that interesting, and advancing the plot seemed... a bit tedious, I suppose. Plus, I think I was put off a bit at the fact that I was playing an open world game, but would constantly use teleportation to get around because the intervening space wasn't worth traversing. Not that teleportation itself is bad, I think; but the way it was handled in Morrowind seemed off, somehow. Like it cheapened exploration, turning that act into a chore that you do when you couldn't teleport to your destination. So, to me, Morrowind had a lot of DF's adventure mode flaws, but with neither the interesting combat system, nor the ability to regen a fresh, random world if I wanted a fresh start.
That being said, I think that having more interesting procedurally generated content IS a worthwhile thing to work for. I'd love to have more variation in the worlds I generate! Such as having the specifics of history actually matter, for some reason, rather than merely being a means to seed the world with quests. Or random wildlife! Rather than every world having wolves, dingoes, camels and ibexes, perhaps some worlds might have large predators that posed a threat through physical size, others might have passive behemoths that dangerous to attack but can provide great armor, still others might have various creatures with syndrome-bearing blood (and not all harmful, necessarily!), and so on. Of course, the cool thing is that I can in theory mod that in myself, if I write an external script that handles both world gen AND creature alteration. Although, in practice, that might be rather hard to do well.