Fun book. We have it in our young adult collection. After listening/reading Neverwhere by Neil Gaiman, which is mentioned in the acknowledgments of this book, I was wondering if this could possibly compare. And, well, it doesn't. But that's a good thing. 
 Un Lun Dun holds its own with an imaginative look at a world unlike our own, though not so different that the reader can't picture it. It even has drawings, which really are quite enjoyable and add to the book (you'll never look at a giraffe the same way). 
 The story, written in very short chapters, moves right along. The characters are entertaining, in an over-the-rainbow sort of way. The names of places and things are fun, too. The power of words and a concern for the environment are part of the story, as well, though not moralizingly so.