Not every ambiguous ending works, but here are the 20 best of them, endings that not only inspired feverish theorizing among fans but ironically felt quite appropriate even without being complete conclusions.
Ambiguous endings and twist endings sometimes, but not always, go hand in hand.
(Warning: Some SPOILERS follow, inasmuch as you can spoil something that is unclear and open to multiple interpretations.)
Audiences may expect to sit down to a movie — no matter the genre — and get a full story that has a definitive conclusion.