We did have rewalling (sort of) in the 2D version - you just had to get creative:
STEP 1: Build a raisable bridge (even 1x1 worked if I remember correctly)
STEP 2: Build a lever
STEP 3: Connect the bridge to the lever
STEP 4: Pull the lever
STEP 5: Dismantle the lever
...aaand you've got yourself something as good as a wall (except for anti-cavein support, but I guess you can't have everything). I've built a pretty big city this way so I can confirm that while it's VERY accident prone, it works. Actually, I guess it may still be a good idea for wall constructions if you want to conserve your resources AND give your dwarves a "wall" with a quality rating to admire.
What I miss the most about the 2D version is the sense of having a goal - survive (farming was more difficult, or seemed so at least - and you had to watch out for attacks not only from the outside, but from the inside as well), dig deep, overcome the obstacles, kill the demons and mine out adamantine and make something awesome for your adventurer out of it before the fort gets too deeped. After that, game over. Oh, sure - most of the fortresses never actually got to the end, but the ultimate goal was always there and even if you've made a "hey, lets just goof off" fort you could still go for the adamantine when you've extracted all the enjoyment you could from it.
Now we get the possibility to build a fort anywhere, in many more ways than before, but the cost is that we've lost that sense of working toward a set goal and goofing off is about all you can do. Oh, sure it's fun too, and I guess you can set your own goals, but it's just not the same.
Still, I love the "build ANYTHING, ANYWHERE, with an EXTRA DIMENSION and an ever increasing list of awesome features" thing that the current 3D releases have going on way more than that sense of a goal of the pre-Z axis versions, so I've switched to them completely and do not look back.
[ May 20, 2008: Message edited by: LordZabujca ]