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.
Anti-Climax Boss: Despite being described as a nigh undetectable race capable of horrible deeds, yet never getting caught, it was very easily to turn all of the Witches in England into mice without the possibility of them using magic to reverse the transformation.
Somewhat justified, in that the witches of the piece mainly employ potions to destroy children. The only act of magic we actually see in the book or movie is the Grand High Witch "frying" one of her subordinates. With no sign of defensive magic, turning their own potion on them makes a degree of sense.
Award Snub: The film failed to get any Academy Award nominations, especially for Angelica Huston's role. It did receive numerous other awards, including Los Angeles Film Critics Association Awards and National Society of Film Critics Awards giving Huston the prize (in a dual nomination for The Grifters.)
Complete Monster: The Grand High Witch, the witches' leader, and easily the most vile and cruel witch that we see. At her meeting with her followers, she wastes no time berating the witches of England for only getting rid of one child a week. She has a plan to get rid of all of the children in England. When one witch gives a shocked exclamation of how impossible that is, the Grand High Witch incinerates her- a practice she makes a habit of at every single meeting she ever attends to keep the other witches on their toes. Her plan is simple: utilize a potion to turn every child in England into mice, and watch their own parents kill them. If a grown up is caught up in it, she says it's too bad for them as well. Amongst a Child Hater race, the Grand High Witch utterly outstrips the other witches in evil and cruelty, and everyone who meets her, from the young hero, to his retired witch hunter grandmother, to her fellow witches, are absolutely terrified by her.
Evil Is Sexy: The Grand High Witch, although averted when she's not wearing her mask.
Esoteric Happy Ending: Subverted. The book seems to be coasting to a happy ending, but turns out more bittersweet. Luke and his grandmother find the main register to all the Witches in the world and intend to turn them into mice, but Luke is still a mouse, with absolutely no prospect of ever turning back into a boy. It's even mentioned that he's only going to live another nine years at the most before he dies, because he's a mouse.
Moral Event Horizon: In the film, if the plan to turn all children in England into mice wasn't horrible enough for you, the Grand High Witch pushes a baby in a carriage down a cliff to draw Luke out.
Most Annoying Sound: Luke's voice in the film. Especially the point where he keeps shrieking "Grandma!"
Nightmare Fuel: Both versions of the Grand High Witch, the book version is filled with heavily implied Fridge Horror of hiding even worse things under her dress just by the fact her face looks rotten. The movie has her being a very hideous depiction of a hag.
Any woman can be a witch, can capture you at anytime and smell you out if you try to hide.
Particularly when female teachers read the book, as Dahl includes a passage that starts something like "perhaps even your lovely teacher is a witch... she might even be smiling!" And every kid in the room suddenly starts inspecting her nostrils and the color of her teeth.
Squick: In the film version, Bruno's father flirting with the Grand High Witch. He hasn't seen what she really looks like but the audience has.
Narm: Good GOD. The pagan dancing featured towards the end is infamous for it. Viewers are shocked by the abrupt Mood Whiplash - the film spends most of its time as a suspenseful thriller only to turn into a fountain of Narm.
Rewatch Bonus: Astute viewers will notice that Ms Mayfield doesn't start to experience magical hallucinations after she has talked with Stephanie about witches.