Though you can see hints of the storylines that have been developed by film and TV adaptations, Shelly's original is nearly unrecognizable if you grew up with the popular culture Frankenstein's monster. The focus on how to construct a man from spare parts was more visually appealing I suppose, so it takes up a great deal of screen-time. Shelly's story nearly ignores it entirely. Also the idea of a grunting, groaning, non-verbal monster was a modern contrivance.
From a modern viewpoint, this is a tale of white male privilege and a sense of superiority over the natural world leading to technology that destroys rather than improves life.
It's also a metaphor for parents and their troubled relationship to their children.
It's not what you expect.