"Devils Stay" felt like it could have been more, with less.
Firstly lets establish a simple point, this is a watchable film. Its a South Korean take on "The Exorcist" in many respects and what it does do, it does well. The story is both cleverly crafted and creepily original. Which in turn, is built upon, by excellent performances, from the cast and suitably austere and bleak, cinematography.
What does not work so well, is this film is overly long. This is due to its tendency to both over explain and repeat aspects, of the story. The result, for the viewer, is still a decent cinematic experience but it does see this film, tend to squander, its scare potential.
In summary, a worthwhile horror tale that could have been better again, with a more concise, economical script, that better focused the core story and in so doing, upped the fear factor, for the viewer.