This does have a low height requirement . (48). My son at 3, was at 48 inches (yes, he was huge). This was not his first "big" one... that one was Steel Force a few months prior at Dorney (first giga coaster at 207 feet!)
He liked the launch, and he was tall enough for it at the time... (fwiw, he was almost four!) He wasn't scared or anyting of it, and went on for three times in a row. To date, he has done many coasters!
As for the first timers, its not that bad.. its only about 60 mph in a few seconds... not that scary, just fast! (its almost as fast as a fast car or test track, or Tower of Terror) The inversions aren't that bad, and the corkscrew is pretty decent.
Its a nice coaster for Disney, but I enjoy Incredible Hulk/Kraken better.
RnR is fast, fun and LOUD. You will be glad you will have gone on this... Its not that scary for me,but we are a coasdter family.