Some people may be wondering how the enemy level system exactly works... while most people know that enemies can be both preset and level with the character, I thought you'd appreciate some further details:

A given dungeon might have a level range of 20-30, for instance.
If the first time you enter it you are level 10, It will scale the dungeon to level 20 and stay that way for the rest of your game, even if you come back at level 50.
If the first time you enter it you are level 24, It will scale the dungeon to level 24 and stay that way for the rest of your game, even if you come back at level 50.
If the first time you enter it you are level 45, It will scale the dungeon to level 30 and stay that way for the rest of your game, even if you come back at level 50.

Areas outside of dungeons work almost the same way. They tend to have larger level ranges and do not lock-in. Example:

A given area has a level range of 1-30
At level 1, It will spawn enemies between 1-4, but if you come back at level 10 it will spawn enemies between 1-14, and if you come back at level 40 it will spawn enemies between 1-30 where it is capped.

So there you go, some ares will be all but inaccessible at early levels, but when you get closer to their predesignated level range it will continue to challenge you until you leave the level range. Once you enter an area the enemy levels are locked-in. Farewell frustrating oblivion enemy scaling... you will not be missed!!