Oh, cripes, Robots of Death
has one of the best-developed societies ever visited by the Doctor and his Companion. In a very short time we learn about the kind of society the people on the mining ship come from, what their various motivations are for being there, we get some idea of the politics, what kind of clothing and social norms the people have, and there's a morality play as part of the story (consigning part of society to slavery due to fear of "otherness"). There's some examination of mental illness and post-traumatic disorders, and Leela gets several science lessons.
Honestly, this is one of the best Doctor Who stories ever. I rank it very closely with Genesis of the Daleks
for how it handles questions of ethics and psychology. By not finishing it, you've deprived yourself of some really good material.