This is a direct companion piece to Mitchell's Bone Clocks, so I'd probably advise reading that before this one. Unlike The Bone Clocks and some of Mitchell's other well-known works like Cloud Atlas, Slade House is a slender novella, easily readable in a few sittings. It's a bit less ambitious than what he's known for, though it mimics his usual jumps in narrative viewpoint and timeline. This time he's dealing with straight-up psychological/fantastical horror. And though the story isn't exactly scary per se, it is appropriately unsettling and suspenseful in parts. 
 I actually really enjoyed Slade House as a minor work. It's much more compact and focused than Bone Clocks (a novel I had some issues with), even if it's dealing with much of the same situations and imagery. In a lot of ways, it blends the fantastical and mundane much better than that novel did. Slade House is also the first Mitchell work I can think of where prior knowledge of the world and characters really enhances the narrative. There are a few throw-away "cameos" that you can ignore, but one major character is utterly essential here. And knowing that person from the previous work makes a huge difference here.