Frankenstein is so well known that even if you haven't seen the film, you will know the cadaverous image of Boris Karloff as the monster. Karloff as an icon of cinema history is probably why there have been relatively few remakes of the film - you cannot think of anyone who could actually BE the monster.
Basically we all know the outline of the story, it has become ingrained in our culture. Henry Frankenstein in convinced that he can create a living being from dead bodies, and does so with the help of an assistant (who surprisingly, for me at least, is called Fritz not Igor in the film - though he is an ugly hunchbacked dwarf). Then, the story goes, the monster goes on a rampage. This, like Igor, is also not fully true, Frankenstein's monster kills Fritz only after being tormented by him, and then inadvertently kills a little girl, who he has been playing with by trying to float her on the lake, the way the two of them have been doing with flowers. We are led to what Mary Shelley wanted us to see, that the monster is an innocent who did not ask Frankenstein to create him, rather than a "real" monster. Generally the creature invites compassion rather than fear, and it is his treatment by others that is the real horror of the film.
Karloff's is the really memorable performance of the film. It was made only a few years after the advent of sound and in this film many of the actors are either ex-silent film actors or ex-stage actors. Whatever their background there is a slight tendency to ham things up a little. This is never a big drawback in a horror film, but it is Karloff's understated, silent performance which makes this film a true classic.