If you've ever seen "The Blair Witch Project", then this style will be familiar to you. The movie is presented as a home recording of something that happened as it was experienced by the characters in the movie.
The character of Micah was somewhat difficult to believe. Here's a guy who managed to continue to record footage of escalating paranormal activity, yet he refused to take it seriously and encourages further escalation through his misguided experiments and taunts.
There are no "in your face" monsters in this movie. Most of the fear is generated by your imagination and what you can't see. I think it worked well and was a refreshing change from the special effects laden horror flicks we usually see.