When we first see Rory Culkin in the opening minutes of "Gabriel," the feature-length debut of Lou Howe, there's an alarming uneasiness to his presence. The actor's jittery brown-green eyes suggest a paradoxical state at once fully alert and lost in another world. Culkin remains that way for the duration of the movie, which finds the title character struggling with mental health issues in the wake of his father's suicide and pining for the affections of a long-lost childhood love.