Some great characters are set up, including the titular mad scientist, his assistant, and his former teacher, but we don’t get enough time with them to really appreciate their conflicts and history. I suspect I’d like the book much better because it might go into more detail about the town and the Frankenstein family’s place in it.
I also really liked the visual style of this movie, which begins largely in creepy darkness, but looses much of its horror in broad daylight, before returning to the darkness as the torches and pitchforks come out.
And, it should go without saying, Boris Karloff is great in the wordless (and uncredited!) role of Frankenstein’s Monster. Much like Bela Lugosi in Dracula, you can instantly see how much his choices have stuck in the popular imagination.