**SPOILER BELOW**
I'm an utter, utter wuss about horror movies but this one did not scare me at all. My husband is usually tough about this kind of stuff but he thought it was really scary. I actually laughed at quite a bit of it, especially when she was about to bite his nuts off.
We did watch it in a cinema, and the point you make about the cinema is totally true, especially because from where we were sitting we could hear from the speakers that there were 'audience screams' (similar to canned laughter on comedy shows) overlaid on the soundtrack, which of course made everyone in the cinema scream.
Leonalewisfan, I think you have seen the earlier version. There are two, the earlier iindie version (which is on a lot of pirate copies) has Katie leave the room and the inference is that she has killed Micah. I haven't seen the earlier version but I'm told after Micah disappears she comes upstairs and is catatonic for a while and is then shot by some policemen.
After the independent film was bought by a major studio they tarted it up and gave it a new ending. In the new version Katie follows Micah out of the room but a few seconRAB later Micah's body is thrown across the room towarRAB the camera. A possessed Katie follows him in and the camera cuts out just as she is about to start eating his corpse.
Apparently there is another version which is quite rare where Katie kills Micah and then slits her throat.
I'm guessing you saw the first one, but Micah is dead and he was killed by Katie while she was possessed by the demon in all the versions.
And I hope you sleep too.