To begin with, it's starts with a wonderful idea - that on the other side of a hidden door, a girl finds an "other" world, where her other mother and other father live and where everything is much more interesting. It's a lovely place. Except for the shiny, black buttons that everyone there has instead of eyes. Coraline is immediately wary, and she is right to be so. But we don't have to wait for her to go through the door for things to get strange - it's creepy right out of the gate. Odd things happen, things that when taken out of context mean nothing. But put them in context, and an air of foreboding quickly settles over Coraline's new house.
I really appreciated the tightness and lucidity of the story - especially because it would have been a cinch to let the material run away with itself (Gaiman was writing on very fertile ground). I loved Coraline's creepiness - as an adult, I was never scared, but I would have been as a kid, and I have to admit to a certain amount of edginess every now and then, even as an adult. But the thing I loved most about Coraline was Coraline herself. She's a wonderful, modern, no-fuss girl, very intelligent and very bored. And she's no easy mark for the evil that intrudes upon her world. Unlike her counterpart in the film adaptation (which was nowhere near as good as the book), the literary Coraline is never seduced by the "other" world, as most children would be. She is wise and brave in the face of frightening things, she wins through cleverness twice, and in a lovely, subtle stroke at the end, she learns not to be bored in the mundane world.
Coraline is everything that it could be, and that's saying quite a lot. Neil Gaiman recently won the Newbury Award for his newest book for young readers, The Graveyard Book. Before reading Coraline, I have to admit I was a little doubtful, but based on the strength of the book I just finished, I'm really looking forward to reading whatever Gaiman writes next.
Postscript: I just started The Graveyard Book (I'm on a roll), and I have to say that it's really wonderful so far. :-)