Twists are awesome. Nothing is guaranteed to get people talking about a movie more than some deftly-executed narrative slight-of-hand.
They are a hard thing to get right – there needs to be significant set-up and a narrative justification to suddenly reveal things are not as they seem. Do it right and you have something that improves the movie as it busts its plot apart, like the Statue of Liberty at the end of The Planet Of The Apes. Do it wrong and you invalidate the whole experience and anger the audience, like Ape Lincoln at the end of Tim Burton’s The Planet Of The Apes.