I saw this last night after it being made "Film of the Week" on BBC's Kermode & Mayo film review. It's a film that plays on some of our simplest fears - fear of the dark and fear of the unknown. And whilst I guessed what would happen in quite a few areas, there was one point in the film when I was completely engrossed in Julia's anxiety - like her, I didn't know who to trust and I doubted everything I suspected.
For me, the best thrillers are the ones that create atmosphere and this film does it brilliantly. I felt very uneasy and tense for a large part of it. Belén Rueda was great as Julia and I'm looking forward to seeing more of her ("The Orphanage" is now definitely on my 'to see' list). Just a slight warning if you're squeamish about eyes, there's one scene you might want to avoid, but don't let that put you off the rest of the film!
So why not 5 stars? A few things annoyed me - there's no way Julia would be allowed to stay in that house on her own after everything that happened and then there was the rusty, dark community centre (which, whilst visually and atmospherically great, was not very believable). BUT I have to agree with Mark Kermode's comment on the film: "If you can give me one of these every now and then - a proper, inventive psychological... that is put together with craftsman-like care and attention - that will keep me going."