This one didn't have quite as much impact as the first book for me, probably because I was already well-prepared for the adventure I would be going on... but never-the-less it was excellent.
I thoroughly enjoyed the new characters and creatures and fully appreciated Collins' ability to create surprising twists and turns.
I know some people turn their noses at children's literature, thinking themselves too grown up to appreciate such infantile concepts... but such people underestimate children and the authors that write for them. I remember hearing an interview once with the writers for Sesame Street asking them how they write jokes for kids. The writers responded that they wrote jokes that they themselves found funny. I think the same can be said for children's literature. I know that I myself have taken much from the first to Underland Chronicles and would recommend them to grownups everywhere.