Fancy words? We don't need no stinkin' fancy words. The style of The City of Ember gets plenty across using simple and direct language. Like when Lina asks Granny what pineapple was:
"It was yellow and sweet," said Granny with a dreamy look in her eyes. "I had it four times before we ran out of it." (7.47)
These two sentences convey a whole bunch of feelings—nostalgia, longing, memory, and, of course, tasty tastiness. And yet, none of the words are more than two syllables. That's pretty impressive. DuPrau manages to pack a whole lot of feelings into very simple writing.
Plus, that "dreamy look" description also shows that the style is metaphorical. As in, Granny wasn't actually talking in her sleep, so we're not supposed to take it literally. We also get a whole slew of metaphors when the book turns toward describing the environment. During the long blackout, Lina's freaking out: "But the darkness pressed against her and she couldn't summon her voice. She could hardly breathe" (5.56). Newsflash: darkness has no physical substance, so it can't actually press against you. But it sure felt that way to Lina, and the language of the book reflects that.