My favorite part about this movie is the insight of how demons are manifest. The presence of the "demon" seems to evolve into a stronger existence in sync with Katie's fear and failing trust of her boyfriend Micah. The fact that Micah encourages the paranormal activity throughout the movie seems to make him out to be the true antagonist all along.
Although the predictability shaves points off the entertainment value as a movie, it turns out to make the plot seem more real.
I wasn't expecting to be affected much by this movie after watching the preview but it did leave me with a bit of an edgy feeling the next day at work. The fact that I crawl into and inspect dark tanks for a living didn't help.