[Mezzaluna]

I agree with ChiliBoy; they are dark. My eight-year-old niece has a 4th grade+ reading level and can read Book 1, but it was too scary for her so she put it away. HP is part of the "good vs. evil" genre with Star Wars and LOTR (Tolkien's Lord of the Rings), so there is wonderfully fertile material for discussion with kids. (Can you guess I'm a reading specialist?!) I also see stimulating theological and philosophical discussions for older readers.

I've read all four, and my take is: Book 1, quite good; Book 2, good, but not great; Book 3, very dark and exciting; Book 4, sophisticated and the best yet! With each new volume Rowling's writing generally improves, IMHO. Her characters also become more complex, too. I'm waiting for Book 5, and also for the film in November. (I'm much more excited about the LOTR film in December, though!)