Frankenstein, a movie primarily about how Doctor Henry Frankenstein deals with the fallout of his monster actually coming to life, holds up very well almost ninety years from its release.
Starting with the monster itself, we find a fantastic character. Without any lines of dialogue, the filmmakers and Boris Karloff had to use actions and emotions to display the motivations of the monster, and they did a fantastic job of it. The fear, confusion, and longing that the novel describes are evident in the monster's actions, to the point of pushing the audience to root for him.
The rest of the characters are also a bit of fun. Baron Frankenstein, played by Fred Kerr, was also a hoot. He played a no-nonsense character that functioned well in the comic-relief role needed with Edward Van Sloan's Dr. Wladman and Mae Clarke's Elizabeth being quite serious, even dramatic. Colin Clive, the man who played Doctor Henry, did a decent job in his role as well, pulling off the role of being consumed by his work, even when he desired to be free from it.
The acting, overall, was a touch more theatrical than I would prefer in a horror movie, but it wasn't so distracting that it pulled me out of the film. The film is a ton of fun to watch, but I do have to say it isn't exactly terrifying. The atmospheric creepiness is somewhat lacking compared to modern-era horror, even going back fifty years. That being said, the movie, if thought about and rewatched, does a good job of displaying how the fear of the unknown, and letting that fear take over, can be the real monster.