-Fallout 3 which had the greatest scaling ever created for a videogame where while enemies got stronger you outpaced them and soon you would fight hoards of them as quickly as you used to dispatch one.
If I remember correctly, Fallout 3's level scaling was actually smarter than that. Every area had a range of levels that would determine the enemies you found in it and their equipment. Undiscovered areas would increase in level as you did too, until you encountered them and 'locked in' their level. This meant that you could stumble into an area, run away from powerful enemies, and then come back when you're at a higher level to destroy them. Additionally every area was set to scale at the different rates or start at the different levels, so some areas would be piss easy if you stumbled upon them at high levels while others would completely destroy you if you encountered them at level 1. The idea is obviously to have some kind of level progression moving across the map, but the game tweaks the areas so that you're likely to encounter something that's balanced for your level.
...
Mind you I haven't found much on Fallout 3's scaling system besides some vague info based on Bethesda's press releases so take this with a grain of salt. But I'm reminded of my experiences where I stumbled upon an area that I was vastly overleveled for. As such the game used the most difficult encounters and enemies for that area which were little more than fodder for my character. So some kind of smart level-scaling was used. I'm pretty sure that the DLCs had this form of scaling too, except they used stupidly tanky and annoying monsters for their encounters which ruined the entire purpose of it.
What they said about "locking" doesn't seem to reflect reality. This "level lock" also doesn't seem to be stored anywhere and modders make no mention of it, or how to reset it. I'm inclined to believe that this never happens.
What Fallout 3 (and NV)
does seem to have is a range of levels that enemies scale to. So, for example, if you go to the areas with the gangs that use laser weapons, they're minimum level 10 if you're lower than that, and match your level up to let's say level 15. And even if you're level 50, they're still at level 15. And so on.
So instead of finding bandits in power armor and fat mans (fat men?) there's a sweet spot where they're an even match for you. And areas do have a difficulty level, but it bends slightly.
That is until the DLC adds Albino Radscorpions which just don't give a fuck.
EDIT: The DLC that add new areas seem to have the full scaling because the game has no idea at which level you're going to travel there. You can beat OWB at level 5 or at level 30. You'll probably get crappy loot if you do it earlier, and some bosses could turn out to be REALLY hard, but the respawning enemies seem to match your level pretty closely.