Bethany: If you come to Six Flags and skip the tallest roller-coaster in the world, is it even worth the trip? I'd argue no. Kingda Ka is different from other roller-coasters in the park because it uses a hydraulic launch system to go from 0 to 128 miles per hour in three seconds. I didn't think it was possible for me to breathe a sigh of relief as we ascended the 456-foot-tall hill, but that's how scary those three seconds were. All that being said, riders looking for that stomach-dropping feeling may be disappointed. You don't really get that here, despite coming down at a 90-degree angle.