Not terrible not perfect but very good actually.
The person who keeps attacking this film and describing it as terrible is being very harsh in my opinion, each to their own I guess, but they are attacking the film in the laziest sense by saying it has nothing to do with the book. I'm a huge Highsmith fan and a) i think it is quite faithful and respectful to the novel as film adaptations go and b) the original book was written in the 60's and although brilliant is slightly dated in my opinion and therefore I enjoyed the modern take on this novel. Jamie Thraves the writer and director of this movie directed one of my favourite pop videos of all time Radiohead's 'Just', I think he shows great restraint in this and pulls off some nice refreshing touches.
In the novel Nicki is very shrill and over the top, I think the director and Caroline Dhavernas do a great job of making her a tragic, hateful and sympathetic character. If taken as more of a bad dream the film makes a lot more sense, at one point Robert says of the fight with Greg, "It was like something out of a cowboy movie" and in the fight scene itself there are shots that remind one of Leone, the fist clenching as if ready to draw. It also has touches of Lynch and Cronenberg, though granted Thraves isn't quite in their league, it's not much of a thriller but I don't think Thraves was going for that, what it does have is great creeping menace. I love Paddy Considine and I think his American accent is really good in this, as good as if not better than Tim Roth's and Gary Oldman's if you ask me.
There are great performances throughout. I've read Highsmith's biography 'Beautiful Shadow' and Cry Of The Owl seems to be one of her more personal novels as Highsmith herself briefly stalked a young girl once and I think this movie version taps into that somewhat. I like the subject matter of fate and death, how Robert is clearly afraid of fate and afraid of Jenny when he finally meets her, she's even more nuts than him! As for the ending, well it's really close to the book, I would have preferred to have ended on the knife not being picked up as it always gave me a chill in the novel but Robert ending up on the other side of the window is like a mirror shot of the beginning and I thought that was quite interesting. The film has a very British sense of humour which is somewhat odd at times but it still managed to make me laugh. Thraves is clearly a cinephile and I think there's more going on in this film than meets the eye.