Hi!
Personally, I don't think that
Ultima belongs there, judging from my experiences with Ultima III, V, and VI. They were regular RPGs and thus a completely different genre (adventure mode of
DF is a roguelike which is definitely a different class of RPG).
In my book, the only game getting closest to fortress mode (sorry, not an ardent adventure mode player) would be
SimCity. Actually, when you look at the original
SimCity, it had an exploratory spirit to it very similar to
DF.
However, the original
SimCity was limited by the computers of that time, and the later versions have seemingly suffered from mainstreaming. While they did improve, only little of the improvements seemed to be in the vein of the original design goal while a lot of improvement seemed to focus on graphics and additional buildings.
SimCity 4 Deluxe comes closest to
DF among the
SimCity games I know, but it still lacks a lot of the complexity of
DF. Had the new features of
SimCity Societies been added to the basic gameplay of
SimCity 4 Deluxe, the result would have been very close to
DF in complexity and quality, but unfortunately,
SimCity Societies is more of a sequel to
CityLife rather than
SimCity and lacks virtually all the interesting features of basic gameplay which had been there all along.
All other games in a similar construction vein I know (
A4,
Transport Tycoon,
SimuTrans) have even much less detail than
DF.
But as people pointed out, in the end, it is just one genre (or mix of genres) that
DF dominates, and it will never cause me to doubt
勇者じゃないモン!, which I consider one of the funniest freeware RPG parodies I ever played and should really play again one of these days.
Deathworks