So, really enjoyed this if I'm being honest.
It's nice to see a film where they are not using the sudden loud noises to scare you (although that does happen once).
You have a plot with no real beginning - something happens, somebody starts to get followed and although there is some explanation the origin of everything is left unclear.
Some of the sequences are genuinly scary, the music certainly adds to this, but that music plays at the exact right moments - it is what you see on screen and not what you hear that frightens.
There are some "not quite so good" parts - a setting towards the end, it's never really explained why they decided to go to a certain place, well it kind of.....
cannot really say any more, but the suggestion seems to come out of nowhere.
A brave ending for a film I'm assuming is going to be launched in the US - we all know they like a beginning, middle and a conclusive end - so a film with very little early explanation, and a far from conclusive ending I'm sure will annoy them.
I personally really enjoyed it, well worth a watch.