I believe Diana Wynne Jones' writing is awesome and I do like this book. The sense of magic in it was delicious and some characters were a joy to read! But I felt slightly disappointed in the end. 
 First off, as I said, the sense of magic was really great and interesting to read about. I don't feel like there had to be an exact explanation as to why these people could use magic, because why can't Magic just be? There is a phrase or two though that does sort of hint as to why there is magic though. I also thought the faerie beings were a joy! Very imaginative. However, when it came down to a few characters, particularly Mr. & Mrs. Stock, i downright hated them for the most part. Every time they showed up they just made me angry and I couldn't understand why they were never given the boot. 
 (view spoiler)[ There were a couple of other things that I wish could have been better explained as well. For example, the enchanted glass. By the end of the book I still didn't understand the exact purpose of it and it never was explained. It did hint to some things but why not just explain it if it's the title of the book? The ending was somewhat disappointing too. Maybe it's my lack of knowledge of Faerie mythology, but the Fete scene sort of fell flat for me. I didn't understand who the tree represented. I didn't really like the last chapter either. It was okay but the very last surprise didn't cut it either. (hide spoiler)] 
 Other than those few things, I thought the book was at times exciting and fun to read. It was charming and with enough mystery to keep me interested.