I went there yesterday for the first time. I was a bit underwhelmed, but the Cornball Express is awesome. What a surprisingly great ride. That's the best airtime I've ever had, especially in the back.
IB itself is old and dirty, and many of the ride ops are grouchy. It's such a contrast to the friendly, immaculate Holiday World, which I visited last week. I didn't stay until dark though. I hear you really have to experience IB at night to get the full effect.
I think IB would be a great place to film a horror movie. It has a slighty evil ambience to it, which I kinda like.
The haunted house is worth the extra money, and the dark ride is fun as well.