Compare 3 Horror Films...

As part of my research I looked into 3 opening sequences of horror films and compared them to one another.
The first film is called Possession, this is a fairly recent film that has been brought out on DVD. The beginning shows a sort of back story behind the film. Although it doesn't tell is much about the time and place or who the woman is, we can gather that the lady was possessed by the box in her house. She does not open it but we can clearly see was trying to destroy it, but it had hold of her. Not long after, she dies and the opening credits appear.
The second horror film I looked at was called Grave Encounters, unlike Possession, this film is more of a documentary type film. The opening shows a group of ghost hunters setting up cameras and technical paranormal activity equipment in an old psychiatric hospital, it shows them finding where its most haunted and where most paranormal activities occur. Its filmed through the perspective on the TV show camera and also through on of the team members hand held camera. This doesn't tell any kind of story or back story like Possession does.
The last film I looked at was called Stay Alive, this film is what I have previously looked at in the 3 Act Structure. Compared to the other two films, this one is more like Possession, this sets up the story. Although its not a back story or what has/had previously happened. This starts with a man playing a new game he has got. Then we see he has died in this game, we see that he was pushed off a banister and hung. After playing and dying, he calls his friend. Then later on, he dies the same way he was seen in the game. As an audience we can connect these two together, but it only sets up the basics of the film, and we only briefly meet the main character.
All 3 films are very different with how they set up the film and whether or not they add the backstory first. The two that are similar are Possession and Stay Alive  in the way that they are filmed and the way they portray the film. Grave Encounters is different because of the style it was filmed in and that there was no backstory or leading story.