Let The Right One In
Not really a horror film, more a gritty Swedish social drama with a vampire love story bolted on.
What makes it so effective is the realism - the backdrop of bleak winter weather and grey functional buildings - and the touching relationship between the bullied boy and vampire girl.
The film is also a well-constructed thriller: director Tomas Alfredson deliberately holds shots for too long to create a feeling of unease in the viewer. During the climax, at a swimming baths, there is an underwater shot which will become a classic of cinema and will be imitated (badly) many times by Hollywood hacks.
This is a film which lingers in the memory and is, without doubt, one of the best of the year so far.