It's important to remember that, when these cartoons were made in 1966, space flight was still in its infancy. We had not even made it to the moon at that time. Consequently, space flight-related shows were all over the air waves. Many of them, like the "Space Ghost" cartoons, were deliberately of a less serious nature, to avoid frightening their young audiences. ("Jonny Quest" was something of an exception.) Still, with characters designed by Alex Toth, and music by Hoyt Curtin, not to mention such voice talents as Gary Owns, Don Messick, and Vic Perrin (also known as the "control voice" of "The Outer Limits"), it's not surprising that this original series went on to achieve cult status.
Sadly, the succeeding versions of the series simply did not live up to the high quality of the original. Instead, they slipped into the trap of overacting, especially in the narration that opened and closed each episode of the later versions of the series. It is sadly unlikely that we will ever see cartoons of this quality again.