There is a difference between the feeling of an open/closed world and the game world actually being open/closed.
I’m talking about the latter, i.e. in an open world I can visit a lot of locations at will.
(btw. the tri-island part of MI2 IMO counts as proper open world)
The emptiness problem mainly occurs at the end of such a section when a lot of puzzle chains have been solved and NPCs have nothing new to say. Barriers won’t change this aspect.
They actually did close TWP at the end, e.g. shops were closed and you couldn’t visit all map locations anymore. But there was no game world reason for it so it felt more artificial (but for TWP specifically this artificial feeling at the end isn’t a bad thing).
I think that for a writer is relatively easy to justify in some way the fact that the world is partially closing. For example, in Thimbleweed Park Chuck has decided to plow under the entire town and build a server farm in its place. It would have been easy to explain to the player that the access to the (de)construction site was forbidden.
With “barriers” you control when a puzzle is/will be solved. If you chose them clever, you “spread” the puzzles over the time. So you have more puzzles to solve at the end of the game and the world isn’t such empty.
Extreme simple example: Let’s assume you need a chainsaw for the final scene. Now you can let the player pick up that chainsaw at the beginning of the game in the first room. Or you can introduce a ranger, selling the chainsaw at the end of the game. So the world wouldn’t be that empty.
Yes, and the world is still very “big”: You have the map and you can walk from the town to the factory and the wood and so on. You still see the buildings in the town, so it seems to be still a large world.
Another way would be to make the factory bigger, close the door behind the protagonists and move some of the puzzles into the factory. So you “cut” the town from the last quarter of the game.
I think that a great answer to your original question has to involve necessarily the presence of two different difficulties.
Given that, everything is probably easier from a gameplay perspective, since the easy mode consists in excluding objects, puzzles and locations from the whole game (normal mode).
The normal mode can have all the wide world with things to explore in parallel.
No easy way out from this choice, and I think it’s a good choice.
You could also just close the streets and say there’s a demo
But that’s what you are doing the whole time: solving puzzles and step for step the world (naturally) becomes more empty. That’s how adventure games work.
And that’s what it makes it feel empty and non-alive.
Btw. what I really hate with such open world scenarios are obsolete NPC interactions, e.g. at the end of a game hell broke loose, Apocalypse whatever, and this old lady in “start-town” still thanks me for saving her kitty…