I've been thinking about the way that most modern RPGs scale the enemies to your level.
This is more obvious in some games, like the Elder Scrolls games, where you'll just randomly start running into bandits wearing diamond plate mail and demons summoned from... well, it's unclear how they got here, but they want to kill you.
It's super prevalent. For example, in Dragon's Dogma, the enemies remain the same category, but scale by level. So if there were wolves in this clearing at level 2, there are a crap-ton of dire wolves in the clearing at level 22.
I would like to argue that scaling up the enemies by the player's level is a bad idea.
The argument in favor of scaling is that it keeps the pressure on just the right amount all the time. The designers can say "this area should be kinda hard", and it'll always be kinda hard, assuming your scaling method is decent. Without it, a player may overlevel and get bored of combat.
Old RPGs used a gating system, where any given area was a specific level. You could (and sometimes had to) level there, but the games had a diminishing returns situation: after you got a few levels ahead, the enemies simply didn't give you enough XP to get to any higher levels. And there's no real way to get the next grade of equipment, either: it's just not in the shops.
In this way, the old games could cap your grind ability, allowing people who want to grind to get some advantage while letting people who don't want to grind squeak through and catch up in the next area, where the old tier is achieved and surpassed in a flash.
But open-world games are not able to do that. If you can walk anywhere, then having areas which are higher- or lower-level effectively act as really irritating blockades: "Oh, you want to walk to the capital? Well, there's a dragon in the way! Nya-ha-ha, it's just a random encounter, too!"
So, instead, everywhere you go you will be faced by enemies that are just the right amount of challenge! GEEEEENIUS!
...Except, no, it isn't. It makes playing the game pointless. Why bother to play any of the sidequests when grinding and leveling up just makes the game harder?
For example, in Dragon's Dogma (which I'm specifically talking about because I recently played it), your character and your job class gain levels separately. I decided I wanted to try out a new job class - the mystic knight. Fine, right?
Except that the enemies are scaled by character level. So even though I'm this total wussy level 1 magic knight, I'm facing down multiple ogres at one time and other bullshit. The other party members are useless no matter what their level, of course.
This is the core of the issue. Not only is leveling up pointless because the enemies keep up, but if your character is not built to be minmaxed at combat, the combat rapidly becomes harder and harder and harder.
The other classic example is trying to play an Elder Scroll game as an herbalist or some other largely noncombat class: you're gloating over the way your speech skill is now 150, but then a dragon comes out of the sky and eats you. Since your "kill everything" skill is still at 3, where it started, you die.
It's crap. It's bad. It doesn't let me play the game the way I want to play it, instead it forces me to play the game like you want me to play it. And if I try to explore other kinds of play, it teases me by initially letting me, but then making the game too hard to continue.
That's crappy. Bad.
But... making zones where the levels are ten times your level is just as bad. It's not really open world at all. It's closed-world with really irritating walls.
My recommendation is to make the world open, but make it clear what combat level the zones are. Then make it possible to skip those zones for a small fee.
For example, you could walk to the capital, but there's level 100 monsters on that path! Well, people go to the capital all the time, so you could also fork over a few gold coins and take the train.
Of course, if there's a mission out in the wilderness outside the capital, you won't be able to accomplish it by taking the train... maybe you'll have to come back later, when your level is high enough.
This has to be combined with A) a speedbump rule, because fighting radically uneven battles is boring, and B) nonstatic level progression. That is, a level 100 baker can't get 0 XP for fighting a desperate battle against a level 10 goblin. Otherwise, a character not optimized for combat will never be able to achieve a level high enough to take on the enemies in a given area.