Well, my wife and I are coaster fanatics (we have been on over 200 different coasters in five countries), and we both loved the Mummy. It is definitely not your traditional roller coaster; it can more accurately be described as a high-tech "dark ride" with coaster elements. "Dark rides" are any fun/haunted-type houses where you ride in a car instead of walk - a la Disney's or Knoebels' Haunted Mansions, or even Spiderman at IOA.
I admit I have a soft spot for this type of ride, and love even the real cheesy ones. They used to be a staple of every regional amusement park (I grew up on the "Flight to Mars", a real precurser to ROTM, at Boblo Island), and even carnival's had them. Today, there aren't many left, outside of the United Kingdom, anyway.
Having said that, we did not find the Mummy "scary" - more like "fun". But then, we've been on the tallest and fastest rides ever built, and don't find those scary either ...