The Curse of Peladon is another episode that I remember watching when I was young. The clearest memory is of the Doctor lulling the creature Agador using a hypnotic spinning mirror and an alien lullaby.
The episode is of interest to those exploring the intersection of Doctor Who and religion, as well as from a postcolonial perspective. King Peladon, of the planet Peladon, is seeking to lead his planet into membership in a galactic federation – trying to help it “raise itself from the dark ages.” There are those who oppose this, fearing that the ways of the federation will sweep aside Peladon’s tradition. Words like “superstition” get bandied about, and the high priest of Agador is one of the opponents of the king’s plan to join the federation. The question of whether the more “enlightened” views of more technologically advanced civilizations are “better” is raised, and the answer is somewhat ambiguous. On the one hand, the Doctor seems as dismissive of superstition as anyone, gets accused of desecrating the “holy of holies,” and demonstrates that Agador is in fact a real creature and a friendly one when appropriately soothed. On the other hand, when a native of the planet says it is better to be a cave-dweller and free, that resonates with us, and we see that moral corruption is not just an issue on Peladon, and not something that the technologically superior and less superstitious members of the federation have eliminated.
I liked that the Ice Warriors were members of the federation, and the possibility of a longstanding hostile force eventually reaching a peaceful co-existence was taken seriously (even if later episodes backtracked on this). Too often, regularly-appearing enemies are simply cardboard cutout villains, ones that are a constant menace with whom it is impossible to reason. That demonization of enemies is dangerous, and so I appreciate when Doctor Who avoids simplistic directions and explores complexities closer to real life.
On a related note, in case you have not heard, there are rumors that a very large number of lost Doctor Who episodes may have been recovered!