The first thing that needs to be said is that Rankin/Bass are to the Christmas special what Cecil B. DeMille is to the biblical epic. They go big and more often not they create a classic in the process.
They always bring great voice talent into the equation and in this special they had the talents of Mr. Jimmy Durante as the narrator. While many of this generation may not know Jimmy Durante from anything else he will be immortalized to many from this special alone. Having a storyteller adds a certain magical quality to these tales and the right casting choice accentuates it.
This tale creates its villain on the spur of the moment, there is no overtly evil entity at play. It is merely that the magician Professor Hinkle sees the hat is magic and greed takes over.
It also starts on the last day of school before Christmas break so the kids in the mix are free to pursue their adventure, which mainly consists of getting Frosty (also brilliantly voiced by Jackie Vernon) to the North Pole.
This special also features a spectacular apparent defeat as it really seems that all has been lost. There is just something magical to a child, and the child in us all, about a snowman and the personification thereof is a nearly fail-safe formula.