If I was going to rate this book only on characterization and dialogue I would give it a five. If I was going to rate it only on plot and theme I would give it a two. So I'm compromising on three.
Brigit and Pidge, two charmingly rendered Irish children, are sent on a quest for no apparent reason by the Dagda, and for six hundred plus pages they wander rather passively around fairy being laconically either opposed or assisted by an enormous cast of characters, most of them absolutely delightful. Then there is a fight. Then they go home.
Mostly the plot is just an excuse for the kids to travel around and meet people and animals and have conversations with them which are filled with the most terrific lyric Irish language and utterly funny, marvelous images and ideas. Much of the behavior of both the villains and the heroes is slapstick funny, some of it is quite frightening or even beautiful but somehow it just keeps falling apart into these long stretches where nothing in particular happens for page after page after page after...
The logic of the whole thing pretty much escapes me and there was little urgency to the quest, but I enjoyed it greatly in parts - and then I would completely lose interest and stop reading for a day or so. Then I'd pick it up and hit on some marvelous bit of dialogue and that would keep me going for awhile longer. If you love language there is enough wonderfulness in here to be well worth the read. If you are somebody for whom plot is important, this might not work for you.