I just recently got this movie off of Netflix and man it was pretty good.
The movie has kind of a clever approach and takes kind of a neutral stance on the subject and lets the person watching decide for themselves on what is really going on.
It was infact inspired by a true story from a girl in Germany back in the mid 70's. Though I will admit that they did add a few things into the movie that didn't seem to be apart of the real case. And the catholic church even admitted that the girl suffered from severe epilepsy instead of demonic possession.
But nonetheless the movie is still pretty good and has some real creepy moments.
I am not sure about what real exorcisms are like. But if they are anything like what was depicted in this movie it would be enough to scare the bejesus out of me.