I'll toss out one more consideration besides the darkness, disorientation etc. Some of the houses can have parts that could be a problem for those with claustrophobia. For example, last year to leave Jack's house you had to go through a really, really narrow "passage." It was like walking between two giant mattesses that were so close together that you were pushing your way through. Not "scary" in the traditional sense, but for those who don't like confined spaces it might have been bothersome.
I've actually been trampled a bit by the people in front of me in some of the houses. They were freaking about whatever was in front of them and were running me backwards and mowing me down. That didn't happen often enough to be a problem, but it can happen so be aware of it! If you're in a house in a group of overly dramatic screamers in front of you, that's when it's most likely.
Overall you're gonna have a blast!! Every time I see that billboard, after I change my pants from soiling myself I look at the calendar to see how many more days I have to wait before the fright and fun begins.