I'm not a huge horror fan. But I have always liked this movie and recently screened it for my older kids. It has a nice flow to it and while formulaic for the genre', has a certain charm and style. I never got why it wasn't a bigger hit.
I particularly resonated with the depictions of the main character's impotent rage while being bullied, the feeling of powerlessness and alienation. The acting really worked there for me. The film is partly a power fantasy of getting back at every school bully that ever tortured you, as well as a cautionary tale of how alienation opens you up to become vulnerable to be "possesed" by bad motivations, by evil.