A large DF world is approximately the size of the moon, according to one guesstimate. A pocket world is 153 square miles.
But completely exploring even a pocket world would be an immense undertaking. Scale is much less important than depth of content - the first ocean you find might be exciting, but the tenth is just another ocean. And that is where Dwarf Fortress does quite well, with a finely detailed simulation of the world and its history.
Wow, DF is much much larger than I had thought. There is behavior going on in the background in Minecraft, but from my highly non-expert position on both games I suspect that Dwarf Fortress has more intricate background behavior.
"In one sense, because of the game’s procedural design, the entire universe exists at the moment of its creation. In another sense, because the game only renders a player’s immediate surroundings, nothing exists unless there is a human there to witness it."
"Through the use of procedural generation, No Man’s Sky ensures that each planet will be a surprise, even to the programmers. Every creature, AI-guided alien spacecraft, or landscape is a pseudo-random product of the computer program itself. The universe is essentially as unknown to the people who made it as it is to the people who play in it—and ultimately, it is destined to remain that way."
More at:
http://www.theatlantic.com/technology/archive/2016/02/artificial-universe-no-mans-sky/463308/