She destroyed Willow and she destroyed BtVS.
Actually no character escaped a flaying from Marti Noxon's (or should I say Noxious) Pen.
In nearly every Episode she wrote she either tore the heart out of the characters/took them to places we didnt want them to go/made them have some emotional breakdown/have them do some completely out of character action(i.e sleeping with another person) and then she left them as crumpled emotional wrecks. I can barely force myself to rewatch the episodes she wrote because the characters are no longer being true to who they are. BtVs would have been an even better show had Marti's Noxious Pen not been involved.
PS I didnt want to put in a "Classification" but I had to. "Overused" seemed the best fit even though I wanted to put "Talentless" or "Worst Thing to Happen"
PPS Looks like I have to score her as a 1 as it wont let me rate her lower than that...