The first time I read Neverwhere was my last week in high school, which means it's been exactly ten years between readings for me. My yearbook teacher lent me her copy and when I was finished I returned it to her house (school was out forever for me at Charter Oak), leaving it on a green-painted wrought-iron table next to her charmingly bright blue door.
The book plays wonderfully with fantasy, mocking the "normal person finds a magic door and adventure ensues" story-type (which Gaiman himself has been accused of abusing) in a delightful way.
I really love this story; I like how it's constructed, I think the characters are fun and funny, and I'm entranced by the magical underworld that Gaiman is at such pains to describe and drag his readers into. That world is filled with a variety of horrors and charms, with magic light and dark, and all of it is filtered through the fool-or-hero who accidentally stumbled into the wrong door.
I think that's probably the biggest part of why the story works: so many fantasy and sci-fi worlds you see take magic and advanced science as a given - tossing a confused and maybe not-very-smart everyman into the mix means the readers are just as lost and get to discover the world in the same way as the characters do.
I'm glad I finally have my own copy - reading it this Saturday made me realize that I had remembered almost nothing about the story and it's a story well worth keeping in mind.
Gaiman, Neil. Neverwhere. Harper Collins. New York: New York. 2003. (1996)