Peter Ericson’s review published on Letterboxd :
Based on a novel by John Ajvide Lindqvist—which I have not read—and skillfully directed by Tomas Alfredson, "Let the Right One In" uses the vampire myth metaphorically to explore pre-teenage alienation, loneliness, friendship, and love, but it also works as a great horror movie—it contains some gruesome scenes—injecting fresh blood into the vampire-film genre. The contrast between the stark realism and the vampire element is one of the reasons why the film is so effective and mesmerizing; its poetic quality is another. Brilliant performances by Kåre Hedebrant and Lina Leandersson, the two young leads. The cinematography is beautiful and the music eerie, creating a suggestive atmosphere that is enhanced by the snowy setting. There is one makeup effect that is reminiscent of Two-Face in "The Dark Knight", but it actually looks more realistic in this film. The final scene is very sweet and nothing short of perfect. Thematically rich, unpredictable, touching, original, and personal, "Let the Right One In" is the best Swedish film I have seen in a long time.