Good AU fics work with the source material as well as reinvent it. It's always interesting to see familair characters placed in new situations. For example, take Futurama. When it first came out, people accused Bender and/or Fry of being re-hashes of Homer, but since they were in a different setting, they could develop in different ways and act in different ways.

I agree with Sparky about the whole Mary Sue thing. I am ABSOLUTELY FREAKING TIRED of seeing every single OC accused of being one, and seeing so many people throw the term around like confetti on New Year's Day. OC's containing fragments or even good portions of the author's personality is INEVITABLE; and believe it or not, there's NOTHING WRONG WITH THAT as long as the character is grounded and fits with the show's spirit. And I hate "Mary Sue tests". All they really do is encourage people to create Anti-Sues that are equally annoying and contrived, akin to fighting obesity with starvation. And one of the tests even admitted that the system is not perfect, as it said U2 frontman Bono(A REAL PERSON) did very high in the test, and then bluntly came to the defense of a fictional character which apparently also scored high, whom the test-master nonetheless loved.

Some posts are bad.