Some films fail because they only go halfway. "Don't Be Afraid of the Dark" succeeds, but it goes too far.

If you decide to see it, be prepared. As a horror film should be, it's gruesome, tension-filled and you can't tear your eyes from the screen. But it's also cruel, quite depressing and utterly sad.

Written and produced by the masterful Guillermo Del Toro ("Pan's Labyrinth," "Hellboy"), this is a technically top-quality production, and it taps wellsprings of anxiety as chilling as a glacial stream. There's more to a horror movie than the power to make audiences squirm, however. For all its proficient shocks, "Don't Be Afraid" is emotionally unsatisfying. The tone is oppressive. Since the characters have no light or happy range and don't show a capacity for joy, there's little at stake when things go wrong for them.

The film, directed by Troy Nixey, follows young Sally (Bailee Madison) to Blackwood Manor, the gothic mansion being restored by her architect father Alex (Guy Pearce) and his girlfriend Kim (Katie Holmes). This is a bad idea, not just because it's the spookiest house outside of Haunted Hill.

A gruesome prologue showed us the home's deranged first owner luring his maid to the dungeon-like cellar and performing medieval dentistry on the terrified young woman. Worse yet, he carried out the atrocity to appease unseen, whispering creatures sealed up in the subterranean ash pit. The basement is sealed and forgotten over the generations, but as is common in such situations, ignoring a foundation problem only makes things worse.

The film quickly establishes Sally's emotional vulnerability. Her negligent mother shuttles her off to live with her father, who is preoccupied with the ambitious renovation that he hopes will salvage his flagging career. Sally is withdrawn, resentful and anxious, the modern equivalent of a fairy tale orphan. She has difficulty adapting to her new home and rebuffs Kim's awkward efforts to befriend her.

Wandering on her own, Sally discovers the long-hidden basement. Soon there are taunting, hushed voices in the air vents to Sally's bedroom and Alex's straight razor vanishes from his bathroom medicine chest. There will be blood.

Del Toro's script is a perplexing mix of intelligence and patchy, clichéd plotting. It hints at linkages between Sally, who feels caged in her lonely new environment, and the beastly things scuttling through the ductwork. Alex and Kim dismiss Sally's warnings as childish hysteria and her psychiatrist prescribes strong mood medication despite ample evidence that things are seriously awry. The climax takes a cliffhanger that would have worked in mid-story and makes it an unwieldy, unresolved finale.

Most of the film's power comes from repeated scenes of a child in graphic, urgent, life-threatening physical danger. Madison performs the grueling scenes with full commitment, providing an intensity that is consistent throughout the film and completely believable. Yet the film stumbles in repeatedly creating these borderline abusive situations for the young actress, a cheap dramatic effect that will prevent many viewers from engaging with the story.

"Don't Be Afraid of the Dark" works on a baseline level; it will leave most jaws agape. But while your limbic system responds to its jolts, your conscience will take exception.