I love Eva Ibbotson's books. Her style is unmistakable and, despite how familiar each story is and how clearly she is playing to an almost childish sense of wish fulfillment, her defer hand at secondary characters and her obvious love for Europe in the early 20th century elevates her books far above the usual.
The plot is mostly predictable, though Ibbotson has a good eye for cliche and knows when to deploy it and when to avert it.
But it's really the love she has for the world she recreates and the elegance of character delineation that makes me come back to these books, even as an adult, and wish i had read a more of them when I'd been younger.