Grave Encounters greatest strength is in the acting and the amount of shock pumped into every scene. The acting at times can be a bit over the top but it works out. The characters feel real. It's great to watch the cool, in charge, and slightly cocky host Lance Preston trying to keep it together as all hell breaks loose around him. You watch as all the characters slowly break down over the course of the movie all up until the exciting conclusion. There's also a ton of foreshadowing, there's a great payoff if you actually listen and watch closely in the beginning.
It's hard for a horror movie to make an impact, even harder for a found footage movie. The whole thing relies on never breaking the illusion on top of having to scare. Grave Encounters nails everything. The story is interesting, the acting is great, the illusion of it being real is never really broken, the scares come a mile a minute and rely more on atmosphere than gore or surprise. There's a bit of camp to over come at times but nothing that ruins the experience. Grave Encounters is everything a found footage movie should be.