Mr Mitchell is one of my favorite authors right now (along with Robin Sloan [where is his new novel by the way?], Marisha Pessl, Haruki Murakami and Lauren Beukes).
If you haven't read Mr. Mitchell before do not start with Slade House. I would recommend "Black Swan Green" or "The Thousand Autumns of Jacob De Zoet" or even "Number9Dream". Then "Cloud Atlas" then "The Bone Clocks" then you are ready for "Slade House".
I know sounds like too much work, right? Well, Just read one book by Mr. Mitchell and go from there.
On Goodreads I "Slade House" was listed in the horror genre for 'Best of 2015'. I guess that would be right; I am too close to Mr. Mitchell's world/works for me to see it as a horror but apparently I am in the minority. Mr Mitchell was recently interviewed on 'Fresh Air' with the title:
Soul-Sucking Vampires Of David Mitchell's "Slade House"