Producing a great horror sequel (or any sequel for that matter) requires a delicate balancing act on the part of the filmmakers. As the saying goes, a sequel should be exactly the same but different. A director wants to give the audience enough of what it loved from the first movie but create enough of a variation so that viewers don't feel that they're paying twice to see the same movie. Although many sequels achieve this balance, most do not. Many times, for better or worse, a director will make such immense changes to the tone, story, characters, and/or genre in the sequel so as to make it all but unrecognizable from the first movie. Here are are a few examples of horror sequels that do this.
The Curse of the Cat People (1944)
dir. Gunther Von Fritsch and Robert Wise
Perhaps the most divergent sequel on the list, The Curse of the Cat People is a beautiful piece of magic realism. In exploring the imaginary fantasy life of its heroine, Amy Reed (Ann Carter), this movie is a unique coming of age story. Of course, the film that it follows, Cat People, is a tense low budget horror film about a woman, Irena, who turns into a panther and kills people. Upon the request of studio heads to make a follow up to his highly successful horror film, producer Val Lewton decided instead to make a more personal project. He kept the words "Cat People" in the title and a few characters (including the ghost of Irena), but little else from Cat People in this sequel.
Exorcist II: The Heretic (1977)
dir. John Boorman
Like many of John Boorman's projects, this sequel to William Friedkin's seminal The Exorcist seems to have been inspired by insanity. My theory here is that Boorman ingested massive amounts of pcp and then watched The Exorcist, The Good Earth, and "National Geographic Specials" on an endless loop. The resulting dream was the basis for this movie. Although much maligned over the years, this sequel is an interesting watch, if only to see a late seventies vanity project run amok. Replacing the bone chilling demonic possession of the first movie with hypnosis, African high priests and demonic locusts, this movie is downright laughable at times. Although it is beautiful to watch, it is not in the least bit scary. It is amazing that this movie was greenlit at all.
A Nightmare on Elm Street Part 2: Freddy's Revenge (1985)
dir. Jack Sholder
Dream life, long the domain of artier filmmakers such as Bunuel, Cocteau, and Fellini, was brought to the down and dirty world of the slasher movie in the groundbreaking A Nightmare on Elm Street -- a movie in which the killer, Freddie Krueger, slays his victims in their dreams. How do you follow up a slasher movie with such a unique concept? By removing the originality. In this sequel Freddie possesses a teen, Jesse Walsh, who kills people while they're awake. This movie has come to be seen as an allegory for a closeted teen dealing with his sexuality. That's all well and good, but unfortunately, this movie just doesn't have much in the way of scares. Besides, this subject was covered in a much better way in Tobias Funke's seminal work, The Man Inside Me. (side note: I was going to include Friday the 13th: A New Beginning on this list for similar reasons, but the first movie in that series had Jason's mother as the killer. In essence, every movie in that series is incredibly divergent)
The Texas Chainsaw Massacre 2 (1986)
dir. Tobe Hooper
Perhaps knowing he couldn't top the visceral horror of the first film, The Texas Chainsaw Massacre, Tobe Hooper decided to go in a completely different direction with his follow-up. Whereas the first movie was grounded in a tense reality, this movie is over the top in every way imaginable. Despite its gruesome reputation, the first film does not have much in the way of gore. Much of it is implied. This time around Hooper hired the brilliant Tom Savini to do make-up work ('nuff said). The Texas Chainsaw Massacre 2 feels more like a high powered action flick with a sadistically silly tone than a horror picture. Truth be told, this movie has long been a guilty pleasure of mine. No, it's not really scary, but that isn't what Hooper was going for. Comparing these two movies is like comparing apples and a double chainsaw wielding Dennis Hopper.
Evil Dead II: Dead by Dawn (1987)
dir. Sam Raimi
Evil Dead 2 is one of the more famous examples of a divergent sequel. With this sequel to his masterful debut film, The Evil Dead, Sam Raimi's cleverly impish qualities came to full fruition. Although the first movie had its share of humor, this time around Raimi made a straight-up slapstick comedy. So divergent is this movie, in fact, that Raimi filmed new and completely different material for the recap of the first film. I would write more here, but this film has been analyzed so extensively by other folks on the interweb that there ain't much new I can bring to the table.