I really like the way Divinity 2 did it. It's actually a relatively small game space, but they filled it up with alot of content. There is pretty much no wasted space, it's all used for something. Lots of hidden doors, hidden keys, people in secluded places. To me, it's more fun to explore a world like that, compared to something like Skyrim which has way more content but doesn't use it as wisely.
Spot on there!
