As nalidoll has said, time and again, fanfic really is all about playing paper dolls. The difference is really all about how one goes about it.
Most of the objectionable stereotyped-teen fanfic writers, the Sue set, take the paper dolls from the movies and dress them up in things they'd blatantly obviously never wear, and have them boffing either Barbies, or each other, complete with squeaky and horrendous dialogue.
But there are some people who lovingly draw their own dolls from the descriptions in canon, paint them with great artistry upon fine paper, and make elaborately detailed costumes for them, not necessarily lavish, but made with love and a need for perfection. And it's those fics that I wish to seek out, artists writing someone else's characters with more attention to detail and characterization than the original author herself might be doing.