Guillermo del Toro's The Devil's Backbone, about an orphanage in the Spanish Civil War that is haunted by a ghost, is best in its atmospheric first half, when the evil is unexplained and seemingly irrational, and (brilliant touch) a huge bomb lies dormant in the orphanage's courtyard. Later, as we get to know more about the ghost, del Toro tries to replace the sense of mystery with characters that seem to symbolize the various factions of the Spanish Civil War.
It works, imperfectly; we do get caught up in the characters, particularly the oldest orphan, who is infatuated with one of the pretty staffers, the elderly couple running the place, and Jacinto, the young man who originally came from the orphanage and has come back, apparently to destroy it. Del Toro knows how to create characters, to get his actors to play them out persuasively, to provoke our pity and horror when terrible things happen to them. He's not quite as confident at trying to develop how they eventually resolve their various conflicts, but the memory of the first half, our sympathy for his characters, and his gorgeous cinematography carry the film (more or less) through.
I'm not too crazy about the CGI effects (somehow I found them more appropriate in Hellboy, which is a stylized comic-book world, but not here); one scene of the ghost vanishing seems too, well, obvious, and a piece of debris rushing towards the screen to black it out seems like the grossest Hollywood action-flick cliche (the flies, tho, are a cheek-twitching success).
It's not a perfect film, it's only partially successful, but it does stay with you.