To me, the book promised a wonderful comedy, for teaching Eilonwy to be a lady is rather like teaching a pig-keeper to be a prince. Alas, we weren't given a wonderful social comedy on manners vs. an intransigent princess. No, we were given an adventure tale, one where Einlonwy is kidnapped, and so rather than get more Eilonwy, we get far, far less than promised, and to that I object. And what little of her we do get gets shoved into the last few chapters. Boo.
All griping aside, the book moves along wonderfully. It's plot twists feel like twists, yanking you about rather unexpectedly, but otherwise the text is crisp, clear, and enjoyable. The fight scenes are few, which I think rather helps the story rather than harms it. The book suffer a little from, "hey, let's get the gang back together" syndrome, but fortunately, a few members of the gang got pared off, leaving us with a rather more manageable working set.
There are no Lord of the Ring -isms left. This series has fully come into its own, developing along its own way. I rather appreciate the more human-scale dilemmas that the characters face. I guess that the scale would make this a "cozy fantasy," rather than epic.