Long-winded, Dramatic
Gaiman isn't Tolkien, so he's not writing descriptions of trees that take up three whole pages, and he doesn't waste time describing anything that isn't absolutely essential to the story either. However, his sentence structure tends to lean toward the lengthy persuasion, and many of his sentences contain multiple commas or asides before they actually come to a conclusion. The effect this has on the narrative is that it makes it feel more like the boy is actually telling you the story out loud, almost conversationally. For example:
Although I was an imaginative child, prone to nightmares, I had persuaded my parents to take me to Madame Tussauds waxworks in London, when I was six, because I had wanted to visit the Chamber of Horrors, expecting the movie-monster Chambers of Horrors I'd read about in my comics. (2.36)
On the other hand, Gaiman's descriptions are pretty dramatic when he wants to emphasize the other-worldly aspect of the supernatural. Check this out:
Empty eyes stared down at us. Then a voice as featureless as the wind said, "I am the lady of this place. I have been here for such a long time. Since before the little people sacrificed each other on the rocks. My name is my own, child. Not yours. Now leave me be, before I blow you all away." It gestured with a limb like a broken mainsail, and I felt myself shivering. (4.61)
It's tough to imagine a voice "as featureless as the wind," but man does it paint a pretty—and pretty dramatic—picture.