Be advised. I talk about the ending of Paranormal Activity in this blog, soooooo SPOILERS!!!!!!!
If you haven't seen the movie, watching the original ending clip probably won't ruin it for you... but it's most likely best not to watch that either unless you have seen the film already.
Now, it was said that Steven Spielberg, upon seeing "Paranormal Activity," thought that the ending needed a bit more umph, and while, the current "Paranormal Activity" ending leaves us on an abrupt "oh no she didn't" moment, I found it satisfying after such a slow build.
You'll probably agree after seeing what they originally intended for their ending. While more psychologically significant and realistic, it doesn't feel as satisfying to know that Katie waddles into the big bright light in the hallway, only to get put out of her misery.