^ They're not really the same in terms of the arc. Perhaps in the scare tactics and the film structure of the films, I'll grant you that.
"Paranormal Activity 2" is generally considered by hardcore fans inferior to the first one until the ending of the movie. I know I was immensely disappointed by it and not scared at all, in fact I laughed out loud at a lot of the "scary bits" and I almost never do that in a horror movie. The third is an improvement.