Someone makes a major change to a canon story, i.e. Ranma getting a different curse, or a more specific example, in the video game KOTOR, having Revan _not_ lose his/her memories.....yet still rehash canon events for the majority of the story?
I just tried to read through one of said KOTOR fics, and I couldn't even stand it.
Exact dialogue, literally copying quests and writing them up.....couldn't continue reading it at all.
Granted, canon is needed, but just answering stock events with small changes to show how different your Ranma/Revan/whoever is seems like an easy way out to me.