Salem's Lot: The Movie captures about 10% of Stephen King's imaginative horror, but it still is a great horror movie to watch. I have always argued that it is hard to make the transition from a book to a movie, because the movie spoon-feeds and doesn't leave room for what the major source of horror while reading a book is: one's imagination.
In Salem's Lot, the Marsden house, located on top of a hill, is inherently evil. Ben Mears (David Soul), who grew up in Salem's Lot and left to become a successful author, returns to confront the evil that is the Marsden house. Mears says in the movie, "an evil place attracts evil people." The house attracts the fancy of Straker (James Mason) and the unseen Mr. Barlow (Reggie Nalder), who open an antique store in the little town. However, Mr. Barlow is really a vampire, and along with his servant's help, he slowly starts turning the denizens of Salem's lot into his counterparts. Ben Mears, along with the help of a young boy (Lance Kerwin) fascinated with horror, must stop Straker and Mr. Barlow before they completely take over Salem's lot.
The plot is great, but however the execution isn't. There are a few moments of tense action and the periods in between are pretty boring. Some of the most powerful sections in the book, such as the one where the Priest confronts the vampire with the cross, are reduced to seconds in the movie and they lack the punch present in the book. Likewise for many of the other gripping sections of the novel. However, the movie does have its interesting parts, and for something that was filmed in 1979, it does manage to scare you now and then. Worth renting.
A Return to Salem's Lot has a bunch of vampires (who've taken over Salem's Lot) asking an anthropologist to write a bible for them, about them. This movie is definitely not worth renting; heck, it's not worth watching if they paid you to do it.
On second thoughts... a reader wrote and said that it's worth renting so you can laugh at it since it's so cheesy. I suppose there is some merit to that, but you better be in a real generous mood!