Roald Dahl's writing style is a lot of things all at once. It's playful, funny, engaging, hyperbolic, and exaggerated all at the same time. Remember what Matilda says about how children's books should have "funny bits" (7.116)? She tells Miss Honey that "'Children are not so serious as grown-ups and they love to laugh'" (7.117). That's a huge clue to Dahl's style right there. He's writing for an audience that loves to laugh. Matilda may be the one who says it, but Dahl's the one who means it. And we know this because Matilda definitely makes us chuckle.
This is a book for children, and the children reading it are going to have a good time doing so. Although some of the vocabulary is pretty challenging, for the most part Dahl's writing is clearly and plainly laid out—still child-appropriate.
Shmoop thinks Matilda is a fun book to read, and part of that fun comes from the language that Dahl uses. You see, a lot of the time, Dahl relies on clever combos of wordy words to get his points across. Sometimes, like in the below statement by the Trunchbull, the words take on such a rising rhythm that they almost seem to turn into song. Try reading this quotation aloud:
"This clot," boomed the Headmistress, pointing the riding-crop at him like a rapier, "this black-head, this foul carbuncle, this poisonous pustule that you see before you is none other than a disgusting criminal, a denizen of the underworld, a member of the Mafia!" (11.23)
Here, the Trunchbull is trying to insult Bruce. This is supposed to be a scary speech. Especially if you're Bruce. But the speech is also so over the top that it becomes funny, especially to us readers. What did Bruce do again? Oh yeah. Steal cake. On the scale of crimes being committed in this book, that's pretty low.
And yet, for the Trunchbull, the cake-stealing is the worst thing that ever happened. Cue the hyperbole. Look at what she calls Bruce: a "clot," a "blackhead," a "foul carbuncle," and a "poisonous pustule." Nearly all of these terms describe growths. Like zits. So all this fancy-sounding language really just tells Bruce he's like a zit. Sure, she could have just said that, but it would have been a whole lot less hysterical.