When it comes to mockumentary type films, there are basically two kinds: good and bad; there's just not a lot of middle-ground with this particular type of filmmaking. Paranormal Activity, which showed at Slamdance, the wild and crazy drunk cousin to the Sundance Film Festival, falls squarely into the "good" camp -- particularly if your definition of "good" includes "will scare the pants off you" and "I had to sleep with the lights on after watching it."

The central idea of the film is that it purports to show actual footage of, well, paranormal activity, in the home of the two protagonists, Katie and Micah, who are living their normal lives until weird things begin happening in their home. Katie, who believes she's been haunted by an invisible, malevolent being since childhood, fears it's followed her to her new home. Micah isn't quite convinced there's anything unexplainable going on, but he purchases a video camera to record their room at night, in an attempt to capture on film any paranormal activity and try to make sense of it. When the camera actually does capture some weird happenings, Micah is at first rather excited by what they have on film; as things escalate, through, both Katie and Micah fear that the entity haunting Katie could turn violent -- or even deadly.

I don't want to give away any more than that, because Paranormal Activity is the kind of film you just have to see for yourself. Suffice it to say that it sufficiently freaked out those of us who watched the screener in my hotel room in the wee hours of a Sundance night, and that I ended up asking a coworker to crash in my room for the night because I was afraid I wouldn' t be able to get to sleep alone. It's surprising how creepy and realistic the film is -- it was obviously shot on a pretty low budget, yet it's very effective, proof that you don't need to have millions of dollars to make a decent film.

Oren Peli, who wore multiple hats as writer, director, editor, and director of photography on the film, wisely avoids the trap some low-budget horror films succumb to of filling up his film with too many cheese-ball special effects. The effects that are in the film are subtle, used to maximum impact, and quite effective, and I was impressed by the quality of the filmmaking overall. Micah Sloat and Katie Featherston, as the haunted leads in the film, are believably terrified.

I've seen Paranormal Activity compared to Blair Witch (the first one, not the atrociously bad sequel), and that's not an inaccurate barometer against which to measure the film, but the film actually reminded me more of Open Water, which pitted an engaged couple against a vast, endless, shark-infested ocean waiting for rescue. Open Water used the fear of its protagonists to great effect as a backdrop against which all their myriad relationship issues were magnified, and charted an entire arc of grief as they realized rescue would likely not arrive in time. Paranormal Activity uses a similar technique, but traps the leads in a haunted house rather than the ocean, battling an invisible, frightening entity rather than sharks. Like the protagonists in Open Water, Katie and Micah cannot simply escape their situation; the entity, a psychic they consult tells them, will almost certainly simply continue to follow Katie whereever she goes.

Dreamworks just acquired Paranormal Activity, and we'll keep you apprised of when it might be coming to a theater near you. You'll want to bring a friend -- this film is scary as all get out. In the meantime, you can watch the trailer on the film's official website.