I've still got Frankenstein on the brain and one theme I keep on thinking about is the one of appearances and beauty. It feels like Shelley's novel takes a mirror to victorian beauty standards.
As I understand it, victorians believed beauty was tied to virtue and goodness and good breeding. Ugliness was believed to be a sign of wickedness and poverty. I think the best example of this is Elizabeth. Victor's parents notice she's prettier than the other poor children they see and turns out she's the only surviving member of a wealthy family and they adopt her. While its a kind action, they never help the other poor children, but the novel doesn't really criticise them for this.
The creature, due to his appearance is attacked and rejected by society, despite him being kind and intelligent. He becomes cruel, scheming, and violent because of his treatment by society at large. The only person who is kind to him is the old blind man who cannot see what he looks like. Like I feel there is at least this criticism of how people are shaped by their circumstances. That someone who is treated as a monster will become one, that the prejudices of victorian society are what lead to thr actions of the creature who has been brought into a world which as no sympathy for him.
Idk I just really like how the novel plays with ideas of moral complexity and how the way we are perceived affects the way we are treated.