I was terrified of that ride as a child!
That said, my kids never had a problem with it and it has been a favorite of DD's since she was young.
One thing I've always done with my kids that I think has helped them be brave with rides is I am always truthful with them about what to expect. So often, I hear people trying to cajole their kids onto coasters/ haunted houses etc... by telling them it's not scary. But, scary is a personal opinion and if the child ends up scared they stop trusting what you tell them and then getting them on anything can be tough.
I have had great success telling it like it is: for example before riding the HM for the first time I told my kids exactly what to expect (ghosts, things popping up, rooms 'stretching' etc...) But, I also told them that it is all special effects, nothing would touch them/ hurt them etc... and that if they were scared they could just close their eyes/ block their ears/ hold my hand until the ride was over and assured them that whether they liked it or not that they would be fine. Armed with the facts, they were in a position to decide if they wanted to ride or not and were secure in the knowledge that even if they hated something, they would be okay.