We've all met it -- the series that went on Far Too Long. Whether it's from a premise stretched out beyond its inherent elastic properties, or the story morphing into another (and lamer) story, or simply a jump over the shark, there's a place you realize only in hindsight that you should have stopped. While you can't change your past, you can warn others. Do so here.
To allow people the most enjoyment they can, please try to avoid spoilers, even if the event is what goes wrong. Especially then.