INSIDIOUS: B-
The film did well in setting the tone, upping the suspense, keeping the thrill and being genuinely frightening. It was creepy and unsettling as a good horror should be. All performances were fairly solid, with Lin Shaye, Rose Byrne and Patrick Wilson in particularly sticking out.
What weakens an otherwise strong film are the nonsensical and often times foolish seemingly out of character choices of the characters. Elise Rainier is schooled and experienced in her craft. It was clear that she knew the potential of the father passing his abilities on to his son. Why wouldn't proper precaution to prevent him from going into the further have been taken?
Even more irrational is why she would place herself in danger by taking a picture of the possessed father when she did. She was intelligent enough and experienced enough to have waited until she was in the safety of a larger group to have snapped the picture. I didn't buy that she was foolish enough to have caused her own death in that scene. That's the type of mistake a rookie investigator would make. Not someone with years of experience.
The father also knew the importance of not drawing attention to himself once he went after his son and he seemed to do anything and everything TO draw attention to himself. Again a rather nonsensical character choice in order to advance the plot.
These sequence of events felt connived and unnatural. As a result what could have been an A film, gets knocked down to a B-.