Though this featured some interesting bits of suspense, I literally laughed out loud when it ended.
While watching Paranormal Activity, I was less interested in the story and more interested in how the film managed to build suspense through incredibly simple means. Loud noises and doors closing unexpectedly led to some gasps of terror from some people in the audience. Had the film stuck to these simple things, I think it would have turned out better. By far the weakest points of the film where when it lapsed into exposition and horror movie cliches.
I mentioned that I laughed out loud at the ending. Not only did I find it completely ridiculous, but was a complete violation of the rules the film had set out for itself. Any sense of realism established by the Blair Witch Project style cinematography was completely negated in the last 30 seconds of the film. Honestly, it ruined the whole thing for me.