Finally a film that discusses (unknowingly, I believe) the occult theory of the egregors. The egregor consists in wishing something so hard that it becomes reality. It would be by this principle that elements from the astral world are converted into the physical dimension when this element is reinforced by belief.
In Thad’s case, he believes that he has inside him the being that he has always wanted to be: a simple man, direct, who doesn’t ask any questions and acts as he wishes without consideration for others. He has valorized this being so much that it has become reality. However, for it to subside, Thad must continue believing in it. When the murders start once more, he is not sure he admires it as much as before.
Without a doubt, it takes more than such an original idea to realize a good movie. The good acting helps the production and so do the well-used special effects. However, we have trouble believing how George Stark, the evil twin, has gone from "tumor" to what he is today.
The murders are simple and a bit repetitive but this is only a detail. Horror movies have the habit of equipping the heroes with absolutely no useful weapons when they intentionally go and confront their dangerous enemies and Thad isn’t an exception to the rule. If he had died and the film would have presented a surprise ending, Thad would have deserved it. Both of his children are in danger towards the end of the movie and, sadly, we perfectly know that they will survive the incident without a scratch.