I would enjoy seeing z-levels make an appearance in this game. I don't know if that is straying to far from the dungeon keeper vibe, but adding a third-dimension would make the world much more interesting to explore.
It's definitely fun running around on a flat plane, but being able to dig and move vertically really makes a world come alive. Right now I feel as if I'm stuck in a small map and not a generated world.
Just a thought, let me know what you think!