The Slow Reveal is a style of hook where the audience is slowly but surely drawn into the tale through a series of off-kilter hints that all is not what it seems. The Alan Wake videogame is a really good example of this - as is Silent Hill 2, but I'll focus on Alan Wake for now.
It begins with an introduction to the characters as they're traveling to a new town. We're introduced to Alan's wife, his agent, and his problems with the blank page. He has a massive dose of writer's block and so they've rented out a nice little holiday home on a lake in order to find some way to break through that block. The characters themselves are the primary hook. They're interesting enough that we'd like to know more.
Then the little hints that all is not what it seems starts turning up and these hints keep the players interested as we want to know what it's all about. You hear about the woman who desperately tries to keep all the lights working in town. You try to speak to someone who's locked themselves in a toilet in a dark corridor (whose light has stopped working) and you meet a rather creepy woman who stands in the darkest depths of this corridor. The videogame also utilises a really nice lighting engine to really emphasise the difference between light and dark spots - though obviously a Storyteller can't really do that.
Then you head to the resort home - a rather old-fashioned and creepy looking wooden home that alerts us that something is likely to happen soon. You cross a long, rickety-looking bridge, head inside, and night falls. When the lights go out, you're well and truly anticipating something terrible happening, especially since your wife has a fear of the dark.
And it all goes worse from there...
What makes Alan Wake relatively unique among videogames is that every Chapter has another Slow Reveal. Generally that's because it begins with daylight and a little bit of research that builds anticipation for the next chunk of darkness which will bring with it a whole bunch more trouble.
See, the Slow Reveal hooks work because they build in anticipation. When hordes of the dead are running at you, you don't have time to anticipate. You don't have time to let your imagination work or to really get immersed into the situation.
They can be a little trickier with players, though, as players often expect that they should be doing something. It's often better if you begin it with a series of small and mundane goals so that they have some direction and don't wander all around the place purposefully seeking out some Big Bad to track down.
The best Slow Reveal game I did involved a series of adventures for a pair of big city detectives who had moved into a small town. They were all fairly ordinary and standard adventures. A petrol station got robbed by some trailer park trash. A series of jewellery store knock offs was actually a collective insurance fraud. Then they get a tip off at a mine and things just go from bad to worse with a conspiracy mobilising against them as well as some signs of supernatural phenomena. By the time the detectives got out of there, they went home, packed their bags, grabbed their wives, and left town.
Part of what made that work is that the players were happy to just play the police officers and that really sucked them into the mundane side of it. They had gotten so used to thinking like cops and seeing the world as a cop would that the supernatural really jarred them. One police officer even rejected the existence of the supernatural, despite all the sightings, until it was almost too late.