Not bad. I hesitated to read this to Sigourney, thinking it might ruin darkness for her. She got through it just fine, and I actually think the book does a good job of showing that darkness is, well, dark. There's nothing inherently scary or evil about it.
Personally, I found the artwork slightly dull. Colors are muted. Pitch blackness is common. I did like the scenes where a flashlight cuts through the dark revealing at least some detail in a room. Sigourney wasn't impressed with the play of light and dark. Likable, not lovable.