Imagine the plotline, story, to be a shelf. It can be wood, glass, plastic... whatever, depends on the type of story of course. Each writer picks the substance from which they create their shelf.
And then, they pick the supports. In my opinion, the supports equal the writing.
You can have supports with no shelf (PWP, anyone?), but you certainly can't have a shelf with no supports.
In some cases, the supports are stronger than the shelf (Harry Potter); in some cases, the shelf is heavier than the supports, and they either fail completely to hold the shelf, or they make it lopsided and very unsteady (Twilight). Shelves of this persuasion are supported by different supports, which are varied in nature and different than the originals (fanfiction).
If you have a fanfiction, the shelf is going to obviously contain parts of the original shelf, but in order to stand in its own right, the shelf has to have some originality.
In order to make my theory clearer, I'll give some examples from the Twilight fanficdom.
Poughkeepsie, in my opinion, has the most colorful shelf I've ever seen in my life. It's incandescent, shiny, sparkly and aggressively, heartbreakly beautiful. Its supports are nearly invisible, but the more you see of them, the more you want to keep seeing them. In this case, the plot and story are so unique, the only thing that writing can do to them is improve them - and that is certainly what Mrs.TheKing does here. Her writing is prosaic, dreamy, and poignant, and she supports her characters and story so well that the support is barely felt - it's jsut so real. You want to be hugged by Emmett and even knifed by Rosalie; you want to be the piece of cardboard that Edward faithfully taps on, and you yearn to be the pew that Jasper frequents. Everything draws you in, and there's nothing more delicious than being drawn into this masterpiece.
Over The Top's shelf is clear-cut black and white, ebony and ivory, swirling around each other, with the occaisional shot of brilliant rainbow colors. Everything is very outlined - no blurry colors here. The effect is striking - reality mixed with naked feelings that show so clearly, your eyes hurt. Like after staring at something bright for too long, this story will stun you and make you want more more more more more. The supports are simple - smooth ebony. Not only do they do a beautiful job of holding up the shelf, they complement it perfectly. Designer fanfiction, srsly. The stark reality of it all makes you want to blur it up - but you can't, and you'd rather keep it that way. It's jarring, beautiful, sobering and so sharply brilliant it makes you want to cry.
All I Ever Knew has the added privilege of having a flavor, as well as a color. It tastes like smooth reassurance, like sharp unfamiliarity and fundamental lust. The colors are smooth and dark, like chocolate and coffee, green and blue. It's blurred, but on the other hand, it just makes you want to cuddle nonstop with it. The supports are polka-dotted, but not garishly. They add color and clear, singular feelings to the fic, where the plot fails to delineate them. This technique holds alot of potholds, but manyafandom manages to skip over them effortlessly.
This is kinda fun. I'll continue the reviews later, when I have more time. Meanwhile - if I don't get back soon, I'll have you know that I'm glued to the Sims.