These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Works in this franchise with their own YMMV pages:
Draco in Leather Pants: Doug Bradley famously quipped about how much fan mail he gets from women and how they love Pinhead, even though he hasn't done a good, benevolent thing over the course of the entire film franchise.
Villain Decay: Pinhead is a rare inversion. In making him more evil (and usually the main villain) after the second film, the writers also made him less interesting.
That's really only true for the third and fourth films; the fifth, sixth and seventh installments feature Pinhead about as much as the first two and in the eighth, the real Pinhead only shows up at the end.
Adaptation Displacement: The number of fans unaware there was ever a book is astounding. The fact that the book and the film have distinctly different titles doesn't help.
Complete Monster: Frank Cotton was a cruel hedonist before he was taken by the Cenobites. After his escape, he shows no remorse in murdering innocent people to drain them of their vital fluids to repair himself. When his niece Kristy Cotton, finds him, he attempts to rape her. He also murders his own brother and wears his skin as a disguise. When Kristy uncovers the truth, Frank also murders his accomplice and lover Julia with no remorse, taking her life as well. When he's taken by the Cenobites again, Frank languishes in a private hell and sends Kristy letters begging for help...pretending to be her father so she'll come to save him, solely so he can keep her as a sex slave.
Evil Is Sexy: Julia's motivation for choosing bad-boy Frank over his good brother Larry.
There was no budget left to complete the special effects in the first film, so Clive Barker and "a Greek guy" hand-drew them on the film over the course of a weekend. Barker was impressed with the results, considering how much alcohol the two of them had consumed.
During the scene with the Engineer, you can clearly see the tracks the puppet is riding on. Harder to catch in VHS copies, but in HD it's more than visible.
Narm: The excessive number of times it cuts to a flock of birds, plus when Chelsea karate kicks the Host off a balcony. Pinhead's attempt to express fear, in his deep, monotone voice: NO. DON'T. DO THAT.
Narm Charm: Revelations has a low budget that shows, campy acting from overcompensating actors, and a replacement for Doug Bradley playing Pinhead that couldn't be more obvious and distracting if they'd tried. On the other hand, the script is a genuinely clever Call Back to the first two movies that goes out of its way to adhere to their mechanics, characterizes the Cenobytes as the pure Sense Freaks they originally were without all the For the Evulz stuff, and puts new twists on old tricks like a victim of the Cenobytes trying to exchange another for himself only for Pinhead to find the trade worthless. It's like They Just Didn't Care except for the writer, who picked up the caring slack.
One of the reasons for all of the call-backs and references to the first film, is due to the fact that Revelations was originally conceived as a full-on reboot. The low budget and lack of Doug Bradley was due to the fact that they waited so long that the rights were going to expire if they didn't have something made within an ultra-ultra short period of time to get the film made and in theaters (where it played in a single theater as a free showing only once).
Although, Doug Bradley apparently didn't like the script (or at least the version of the script they sent him when he asked). That, combined with how little they wanted to pay him, was the reason he didn't come back.
To be fair, Bradley didn't hate the script either, he just found it to be unfinished. The problem he had with it was Dimension's refusal to make a second draft.
The Woobie: Steven starts as this in Revelations, particularly in the flashbacks when he can't stomach Niko's "needs" anymore and Niko turns on him as a result. And then it turns out he's the second Pinhead.