The problem with most horror sequels in any medium is that they tend to retread old ground, based on the fact that if it worked once, surely it'll work a second time (The Blair Witch Project 2). And a third (Jaws 3D). And a fourth (Paranormal Activity 4). And a seventh (Saw 3D). And a tenth (Jason X).
What do all of the above have in common? They all sucked, sure, but why? Because they added nothing new that hadn't already been done before in the first movie.
Now let's look at the rare horror sequels that worked. The third Exorcist movie, for example. The second Exorcist is so bad that the third ignores it entirely and goes in its own disturbing direction, with probably the best jump scare in cinematic history, along with a legitimately creepy villain played by Brad Dourif. The weakest part of the movie? The actual exorcism scene at the end, which had already been done before in the first movie, and was only in it because executives demanded it. The movie would've been just fine without retreading old ground.
How about Aliens? The movie still had callbacks to the first (good old chestbursters), but it took what the first film had and actionized it. The first one was all about suspense and terror, while the second film ratcheted up the action a notch while still retaining that feeling of dread the first one had, about the potential loss of someone you care for, and the notion that what happened to your friends out in the field could just as well happen to you. It didn't retread old ground, at least not at its expense.
What do the Five Nights at Freddy's sequels do? They all do the same damn thing the first game did, except the animatronics look uglier with each sequel. The best thing you can say about the fourth game is that the setting is your house instead of at a Suck E. Cheese's, and that you can move around...for a few feet. But it doesn't add much new to what the first one had already done. It feels like they just gave up with the jump scares, and said, "I don't know about the new sound effect, just mash the first three screams all together and see what it sounds like. I also read a gross fanfiction called Cupcakes once, so let's get that cupcake in on the action."
