The film's ending lingers in your mind long after it's over.
Tips
history
From Wang Yucheng's poem 《橄榄》 (Song dynasty) on olives: "良久有回味,始觉甘如饴" — after a while the aftertaste comes, and you realize it's sweet as honey. The idiom extends this literal experience to anything memorable.
usage
Works for food (literal) and for books, films, experiences, speeches (figurative). Always positive — something that keeps rewarding reflection.