gāokāidīzǒu búshì zhǐ mà jiéjú érshì shuō zuòpǐn kāishǐ hěn hǎo hòumiàn mànmàn diào xiàqù

高开低走不是只骂结局，而是说作品开始很好，后面慢慢掉下去。

"Starting high and ending low" does not just criticize the ending; it refers to a work that starts off very well but gradually declines later on.