Is it better than the Oblivion system? Yes. Is that saying much? No.
This is how it should be. Every cave/dungeon/ruin will be a certain level when the game starts. The distribution should be a bell curve...such as 50 low level, 100 mid level, and 50 high level. Obviously there would be varying tiers, so chances are even at level 5 you could find a level 10 dungeon that you can still beat. They wouldn't all be level 1, level 25, and level 50.
Now, after you clear a dungeon, it will respawn within a game week, or two. This could vary as well. The enemies that respawn then will be random, though perhaps influenced by your level. So if you are level 40, clear out a level 5 dungeon and come back, it will respawn between level 5-40.
Todd, put down that vault boy figurine and take notes.
I like some aspects of this approach and dislike others. Having a fixed level system for dungeons is initially appealing because it allows the creators of the game to control how much content is available at what level of the game, making sure there are adequate dungeon experiences for your character at each level. However, it also creates a very rigid narrative of how the player is supposed to move through the world, thus leading to the 'hand-holding' effect. In one way or another, strict leveling will put the player's course through the dungeon crawl in the hands of the programmer.
That being said, I do like the idea of dungeons being re-purposed for higher-level quests once completed; save for the fact that all in-world loot will be missing the second time through (you know, the good stuff) and all you will be left with is the level-specific randomized loot coming from containers. Not only that, but why would you want to have the same dungeon experience twice? Didn't we do that ENOUGH in Oblivion? That's a huge draw of Skyrim's dungeons, they are vast and varied! (So we are to expect, anyway...)
Well, I've kind of contradicted my initial post. I am in favor of loot of all levels being available to bold (and sneaky) adventurers who find ways through high-level defenses, but I am not in favor of being told when to go where in the game world (especially if I want to take a few levels to myself and upgrade my town-friendly abilities instead of adventuring). That being said, the lore should be a huge driving factor in getting players to explore new dungeons and specific times. Players should come across books and characters detailing potential adventures (yes, like Morrowind!) at the appropriate levels. Unfortunately, this system might not work as well in an environment like Oblivion where all the locations were cramped together and fast travel made exploration almost a cheat.
The only way to make finding an out-of-the-way, too-high-level-for-me, full-of-precious-endgame-loot discovery enthralling to the player is for it to actually be... out of the way. (Not 30 seconds from a major town that allows fast travel, or immediately in view of the last low-level cave you have explored.) The world must be barren (to some degree) for these discoveries to feel significant. Otherwise, every player might share the same experience of finding rare items in the same places at the same times, and that completely defeats the point of looking for them in the first place.
Ultimately (if you would like a TL;DR, here it is) I think Bethesda is making the right choice with how they are leveling the world, but we have yet to see if it is implemented properly. I change my mind, Bethesda may yet know... exactly what they are doing. Just please, PLEASE BETHESDA, make the highest level loot non-randomized, non-container loot. I want to walk in and be awestruck by a glorious glass axe that entices me into a dungeon experience I might immediately regret, but can't stop attempting. That's when I feel most rewarded, and that's when I feel most appreciative of the items I am going to be using every 30 seconds for the next 200+ hours.
Well... Thoughts? Am I getting warmer?