Marc Savlov of "The Austin Chronicle" called the film "the most intense and original creature feature I've seen in my adult moviegoing life [...] a pure-blood, grade A, exhilarating monster movie". He cites Matt Reeves' direction, the "whip-smart, stylistically invisible" script and the "nearly subconscious evocation of our current paranoid, terror-phobic times" as the keys to the film's success, saying that telling the story through the lens of one character's camera "works fantastically well". Michael Rechtshaffen of "The Hollywood Reporter" called it "chillingly effective", generally praising the effects and the film's "claustrophobic intensity". He said that though the characters "aren't particularly interesting or developed", there was "something refreshing about a monster movie that isn't filled with the usual suspects". Lisa Schwarzbaum of "Entertainment Weekly" said that the film was "surreptitiously subversive, stylistically clever little gem", and that while the characters were "vapid, twenty-something nincompoops" and the acting "appropriately unmemorable", the decision to tell the story through amateur footage was "brilliant". Roger Ebert in the "Chicago Sun-Times" wrote that the film is "pretty scary at times" and cites "unmistakable evocations of 9/11". He concludes that "all in all, it is an effective film, deploying its special effects well and never breaking the illusion that it is all happening as we see it".