With the rise of high-concept and blanket advertising, it's often hard to come to something with no preconceptions, and I think our capacity for genuine surprise as an audience has diminished. Film trailers are particular culprits in this department, but book reviewers are no strangers to the spoiler either.
So, the final act twist seems to offer a perfect compromise - it allows the main premise to be clearly spelled out, while also stoking audience anticipation by mentioning the "astonishing twist ending" in every bit of promotional material.
Unfortunately for me, I view the words "astonishing twist" as nothing less than a challenge - one that I will beat by guessing the ending no later than mid-way through the book/film. Regrettably, this also completely spoils the experience. The zenith/nadir of this came with The Sixth Sense, a film that I deliberately saw at an early preview, avoided reading any reviews of and knew only the following information:
- Bruce Willis helps a boy who sees dead people.
- It has a big twist at the end.
At the other end of the scale is the twist that is so outlandishly stupid that your sense of disbelief explodes in a cloud of purple smoke. The kind of ending that causes you to throw the book across the room or spend five minutes numbly sitting in your seat as the credits roll, thinking about all the gaping plot holes that have swung into view.
A good twist ending reinforces what you liked about a story and makes you see it in a different light. It should be able to utterly surprise you but also to perfectly fit the tone of the story. This is perhaps why really good twists are hard to find, but also worth hanging onto. It's rather ironic that the former king of the twist - M. Night Shyamalan - has had his own surprise reversal by turning into one of the worst film directors in the world. Did anyone see that one coming?