Technically, it's not the first time I read this book. However, the actual first time was some 12 or 13 years ago, and I only had a French translation. I don't like translations.
I had kept good memories of Neverwhere, and fortunately, reading it again didn't change my perception of it. London Below really grew on me. I had no problems at all picturing it, imagining its strange inhabitants, its dark streets, its odd rituals. Those are the kind of themes that appeal to me.
On the downside, I'm a little less forgiving of Richard's character than I was, well, 12 years ago. He doesn't do much, and takes a long time to "grow up". I much preferred the rest of the cast: Door, Hunter, the marquis, and even Croup and Vandemar. (Also, do consider that I give bonus points when a character makes me feel all "hey, I want to draw/him her!".)
(On a sidenote, I'm not giving bonus points for this edition's cover. Couldn't we have a better integrated torch? Uh.)