I also couldn't understand why the main character (Dr Victor Frankenstein) was renamed Henry, and his friend was renamed Victor! At least Elizabeth retained her name. I also couldn't understand why "Henry's" father Baron Frankenstein, kept referring to his son as Frankenstein! Not Henry, or son. There is also a moment when a father finds his murdered daughter (of course killed by the monster, but he doesn't know that), yet he turns up at the Frankenstein residence demanding justice, and a hunt is organised for the monster. We don't see anyone find out about the monster, but magically everyone instantly knows that it killed the girl. I feel this is just sloppy script writing.
What I did like was the way that James Whale used light to create shadows throughout the film. When we first see the monster walk into a room towards Frankenstein, there is a huge shadow cast by a hidden light, in such a way that the ominous shape towers over Henry. There are many other instances of this (such as steep staircases disappearing into shadows) , giving the film a very striking visual style.
Unfortunately I think that for all this style there is too little substance. All of these Universal classic horror films are about 70 minutes long, and while The Wolfman managed to tell a great story I can't help but feel that if Frankenstein had been longer then a better approximation of the source material could have been reached. This would have made a far greater impact and made a much better film in my opinion.