It boggles my mind how nigh-incoherent Dune the Movie is compared to the Dune TV miniseries. The thing that bugs me the most is how the villains were written and directed as raving maniacs who never stop cackling and screaming. Those kinds of characters belong in an asylum scene, drooling on themselves in the background; not as the chief villain faction that is supposed to be a challenge to the hero. I was never really sure what the movie Harkonnens’ plan even was ’til I saw the miniseries: it’s basically summed up in a throwaway line in one scene of the film, while they spend the rest of their screentime mugging to the camera and shrieking like idiots. In the miniseries their purpose is made very clear, and the Harkonnens are believable threats: they’re ruthless and calculating (well, Rabban is just a violent idiot, but he serves a purpose that way).
If half your villain’s scenes consist of him floating in circles, shrieking and laughing for no reason, I’m not gonna take him seriously, nor see him as a credible threat to anyone. Likewise if he’s the sort of sneering lunatic who tortures just for the fun.
Credible villains think they’re the hero of their own story, even if they’re crazy. They don’t exist purely to be pains in the ass.
For example, I knew an author (who’s probably reading this and laughing by now) whose demonic villain made dolls out of people for his equally demonic daughter. The idea was to convey how fucked up the bad guys were, via a gruesome and highly detailed sequence of gutting someone alive, sewing them up, and making them into a grotesque plaything, all while giddy at the prospect of causing pain and death. It made me wonder “what’s the point?”, which is what you should be asking yourself with every scene you write. Does this serve a purpose, or is it just fluff? In this case, the purpose was “lol isn’t this fucked up?”, which isn’t good enough.
More telling and horrifying would be to show that the characters coldly think of humans as so beneath them that they’re like cockroaches are to us. Maybe the daughter finds them amusingly cute, and likes collecting people-dolls for her bedroom. And the dad goes about the task like a taxidermist: cold, callous, something he’s done a million times before without thinking twice about it. But he makes damn good dolls out of these useless creatures because he dotes on his daughter. So now the scene is less about a gory spectacle for kicks, and serves a purpose: it shows how much this depraved bastard loves his little girl, and the author can play on that later in the story if the hero runs afoul of his beloved little girl. If he makes you into a doll for his baby’s entertainment, what’s he gonna do if you pose a threat to her?
Write with purpose. Don’t write fluff.