Blue in Munich
Crocked Professional Yeti Impersonator
Totally random one (and guessing a few will have examples of why I am wrong) but TV shows with more than 6 series. So very few can maintain the quality and so they just drag on, going through the motions until everyone turns off and those that do keep going just become soap operas
And in a similar vein, 6 part series that should have been a decent feature film instead.