It is firmly in the drama, horror, thriller vicinity. But why I rated it so high was the assuredness to the surreally ordered visuals (as is geometry, mis en scene). I found that to form a parallel with a story about people living a very ordered existence. This may not make sense but think Hitchcock's Shadow of a Doubt as told by Bunuel.
Here's a capsule I wrote a while back
Stoker (dir. Park Chan-Wook) 

½
A disturbing thriller that couples an eerie aura of suspense with mathematically precise visual symbolism. The detailed, ordered shots attach a dark underbelly to stoic suburbia reminiscent of David Lynch's Blue Velvet. It's not a complete original, but a very fine mood piece, nonetheless.
I am personally waiting for a $10 price, so I would say $18 is a bit steep for buying something blindly. It's a tough call.