Charles Laughton, the lead actor in the film, plays Sir Humphrey Pengallan. Like with several of the others, the best kind of introduction they could give him is a fancy dinner at a mansion, which comes off as being a satire of the snobbish disposition of the rich. When he comes across Mary Yellen, played by a young Maureen O'Hara, he courts her like he's a character in a Shakespeare play. She becomes a key distraction to the band of smugglers when she's sent to live in the Jamaica Inn, which is filled with men that come off as being quite laughable. You would expect for them to be quite creepy and act like savages, but there was a better chance you would laugh at them instead of jump in a fearful or spooked kind of way.
Robert Newton plays "Jem," who is supposed to be a protagonist among the smugglers living in the inn. Mary rescues him and they make an escape, but their chemistry is a bit fizzy and Mary comes off as being incredibly clueless and confused. Jem is a little bit wiser, but his role is incredibly small to the point that it provides him no opportunity to shine. The scene in which Mary lets the boat into the sea shows that she is quite confused and makes her role as a heroine to be relatively weak. The female roles in this film are quite weak, as Leslie Banks' role as Joss Merlyn shows that her role plays little to no use.
The character that seems to bear the center of attention is Sir Pengallan. He's involved in the only twist (and in essence the only element of horror or thrill in the film) and is given the opportunities to take part in the action of the film. His role was decently developed, but what happens to him is portrayed in such a ridiculous fashion, adding to the notion of the film.
Excuses could be made for the film being made in 1939, such as the delayed effects and different roles in the film, but you know what, The Wizard of Oz was also made in 1939 and it's one of the greatest pictures in film history. The execution of the actual filming was absolutely poor. An entire list of things could be added to the list of absolutely poor elements: the transitions, the character development, our connection to the characters, the story at large, the tension, and the entertainment value only to name a few.
What's even worse is that du Maurier wrote this as a horror novel and the characters were intended to come off as being scary. Hitchcock did a fine job interpreting her other works, such as "The Birds," but he couldn't scare us in anyway with Jamaica Inn. At all costs, Jamaica Inn the movie should be avoided. It's an incredible waste of time and entertainment space in what may make up a little portion of your busy life, just like it is for my own. It's a movie that could have been, but wasn't.