You know a problem I had when watching this film too? Recently I've become addicted to Supernatural
after buying the series on DVD blind and watching all the series straight after one another (I'm currently two episodes into Season 5)
So when watching this movie I was half hoping at some point for Sam & Dean to kick the door in, the Impala outside, shoot the demon with their salt loaded shotguns, start pouring salt over the windows and doors, set up a devils trap near the basement, maybe burn some bones, and Sam uses his Season 4 demon mojo to exorcise Katie and all this black smoke comes out of her mouth, and all the while AC/DC's 'Thunderstruck' is playing in the background.
That would have been a good ending