Overall, not a bad story, if long-winded at times. I am, however, going to delete it from my iPod and never listen to or speak of it again, because I want its memory completely gone from my mind in the event that I need a CAT scan or MRI. So I guess that means the story succeeded as horror?
The first part of the story kind of dragged on. If it had started as he was going to the hospital that would have kept the pace up a little bit better, but that's alright.
I definitely could've done without the historical sections. For one, the transitions between times were not obvious to me, so there was major jarring each time the transitions happened. Also, having a possessor which drives its hosts to do terrible things is less scary to me than just knowing there are crazy sumbitches out there somewhere.