I love plot twists. No coincidence then that once I was introduced to Robert Ludlum at a young age, I quickly worked my way through most of his books.
I try to incorporate twists into The Unearthed books as Eddie's big ah-ha moments that usually propel the story into the final act. But I don't force twists into stories (at least I hope I don't). For example, I wouldn't call the revelations coming near the end of The Hysteria or The Traveler plot twists per se. They're more plot developments.
Plot twists in film are really effective when done well. Of course there's the monumental oh shit moment at the end of Planet of the Apes, where it feels like the story has just sucker-punched you. And when you say plot twist, it's hard not to think of The Sixth Sense or The Usual Suspects, both fantastic films.
But I clearly remember the first really great turn I ever saw in a movie. I was probably ten or eleven, way too young for this movie, but I was watching Marathon Man, SPOILER ALERT - STOP READING NOW, and got to the part where William Devane "rescues" Dustin Hoffman from the evil, sadistic Nazi dentist. Of course Devane is working with the baddies here and just trying to get info out of Hoffman, and when he steers the car right back to the same safe house where Hoffman has just been tortured, it's a great, horrifying moment.
Nothing beats a great plot twist. What are your favorites?