Some films rely solely on atmosphere, and this is one of those.
You keep having the nervy, edgy feeling that something is very wrong throughout the first 40-odd minutes, but what follows is something far more sinister and dark. Even though you feel you saw the twist coming, it's still quite a WTF?! moment - followed by a few more.
Do give this one a spin, if you haven't already.
* * * ½