Well, it depends on what you are talking about -- chunks or regions. Let me give you a fuller picture:
- Smaller: The world map itself only has one continent, rather than many. So no sailing on ships, no infinite exploration in one world. You play, you win or lose, you play another world.
- Larger: The world map itself is vastly larger than one continent was in the old game, though. You can actually set the world size as a setting, but on the default it's maybe the size of 8 or 10 continents in the old game, something like that.
- Feels-Larger: Movement is more restricted on the world map in the new game, making distances feel more significant compared to the first game. Much more satisfying.
- Smaller: Previously, the surface of a region used to be made up of a lot of chunks (6-12+). Now there is only one surface chunk per region, ever.
- Larger: Previously, most of those surface chunks were 128 tiles wide, a few of which were more like 256 tiles. Now all of them are in the neighborhood of 512 tiles wide.
- Feels-Larger: Since you move slower than in the first game, it takes longer to traverse the same number of tiles anyhow. Also, the density of interesting stuff (and combat) is a lot higher than in the first game.
- Smaller: There are far fewer caves and buildings than in the first game, in general.
- Mitigating: This makes the time you spend in them actually more interesting, and it makes it so that you spend more of your time outside, which is also good -- it gives more equal playtime to outside and inside, and less to undergrounds actually.
- Smaller: There are far fewer rooms in each building you go into.
- Larger: Each room is much larger than in the first game, which is great because that makes more interesting rooms and fewer transitions between them.
- Extra Bonus: There are no longer tons of empty rooms, or rooms you need to go randomly grinding through for stashes and so forth. It's now much more goal directed.
And I think those are most of the points. Generally speaking, what you are exploring in this game is the world map primarily, and to do that you explore various regions in a smaller capacity.