The titular character is a well-mannered, preternaturally intelligent 9-year-old (Jacob Kogan) living in a posh Manhattan apartment with his stockbroker dad Brad (Sam Rockwell) and stay-at-home mom Abby (Vera Farmiga), both celebrating the birth of Joshua's sister Lily. But from the earliest scenes, there are ominous hints not only of sibling rivalry but also Abby's history of postpartum depression and both parents' slightly uneasy relationship to their very smart, very strange son. The influence of Polanski and Kubrick is evident not just in the Shining-inspired title cards but in the way Ratliff introduces a psychologically plausible scenario - dad's busy living in an adolescent fantasyland while mom unravels at home - then confounds our expectations in pleasurably disorienting ways. Like the increasingly discordant piece that Joshua plays at a school talent show, Joshua is built of small, curious details - the tension between Abby and Brad's born-again mom, Joshua's interest in mummification - that accumulate in impact as the extent of Joshua's malevolence comes into focus.
Much of Joshua's effectiveness can be attributed to its emphasis on character development, specifically the often terrifying experience of caring for a newborn. The scenes of Abby losing her self-identity and possibly her mind while Brad shrugs off the reality of his situation could make for an effective horror movie on their own, as they touch on emotions that most new parents experience but are rarely given voice in a culture that idealizes childhood to a mindless degree. Ratliff's work in documentaries (his previous film was the brilliant Hell House) serves him well here, his eye for detail and emphasis on emotional realism lending the horror-movie conventions of the film's second half a very credible sense of creepiness. This sense of verisimilitude also gives Ratliff's leads plenty of room to shine, with Rockwell darkly hilarious as a jockish dude increasingly suspicious of his son and Farmiga clearly relishing every frayed nerve and sudden emotional outburst. I was particuarly impressed by a brief, non-sexual moment of nudity as Abby distractedly uses a breast pump; it somehow seemed more vulnerable than any sex scene, and Farmiga allows herself to be so unself-conscious that it speaks so much to a new mom's fragile sense of self-identity.
Kogan isn't quite as effective, though this doesn't reflect the kid's abilities as much as it does the somewhat obvious choice of fitting Joshua into the soft-spoken ominous kid archetype seen in countless post-Shyamalan movies. Joshua does occasionally try a bit too hard, underlying elements of the story that would have best remained somewhat ambiguous. This is particuarly true of the last scene, which spells out what we've just seen a bit too much - it would have been more effective to trim the dialogue between two characters and allow the final image to speak for itself. Still, in a time when horror movies generally bludgeon than they frighten, it's good to see there's still room for the quieter, more internal brand of horror that truly gets under one's skin. In other words, this one's fun for the whole family.