King Ghidorah is the only giant monster not killed during the entire series (not including Godzilla, of course).
Takes place in the same continuity as the original Godzilla series, according to Toho Co., Ltd.
The last appearances of the original King Ghidorah and Gigan (who would return in updated form 31 years later in Godzilla: Final Wars (2004)).
Godzilla guest-stars in Episodes 4, 11, 15, 21 and 25. Gigan fights with Godzilla in Episode 11, and King Ghidorah appeared in a separate two episodes (5 & 6, a two-parter).
Director Jun Fukuda was brought in to direct several episodes, but he didn't have fond memories of the show. When asked about the series in an interview Fukuda simply said, "You don't have to mention that show!"