Its not scary (as in terrifying) if you are an adult. You may get jump scared but that’s only really scary in the moment.
For anyone that has a real phobia it’s a good idea to check out YouTube for info on the house (spiders, things like that, etc) but no there is nothing that would give the average adult actual nightmares (imo).
ETA: You are going through the houses in huge conga lines, the mass of people (usually laughing at being scared) helps keep the mood light.