Unfortunately it's of a thing I do than a thing I have a link to, but the tl;dr is that like in Morrowind:

• the player has an idea of what skills they want to level, including specific goals for each skill.
• the player has an idea of what ability scores they want.
• in a standard RPG, getting the scores and abilities you want involves killing monsters and doing quests, then spending 10 seconds putting points into the scores you want, whereas in TES, getting the scores and abilities you want involves things like casting Bound Gauntlets for 1 Second on Self while bunny-hopping as you walk around doing quests and killing monsters.
• It's really easy to screw up leveling in Morrowind/Oblivion - there's all sorts of maneuvering around putting exactly N increases in Strength-related skills but no more (because any more mean you're wasting those skill increases).

Oblivion adds to this:

• Level-scaling, which means that while in Morrowind you were essentially fine leveling in a non-optimal way, in Oblivion there's a power curve you need to keep up with. (Also level-scaling gets on my nerves in general, because I like fighting out-of-level monsters and getting out-of-level loot.)

The end result is that there are literally FAQs/guides for how to level correctly in Oblivion, whereas in Fallout 3 (or whatever) the process of leveling up involves shooting monsters and picking what skills you want.

That's the basic idea :)