Perhaps you could narrow your question down a bit as this is a very broad question to ask.
Even though Harry Potter is a character originally written for children, I have enjoyed all of the books immensely. I am, in fact, currently reading the first book to my daughter who will be going in to first grade in the fall. I have enjoyed the later books more than the first one since the stories have become more complex and the writing has sounded less like it is aimed at 10 year olds, but I still like all the books.
I think that the books are great fun and I think that they convey positive messages for children.
Is there some particular aspect of the books or the characters you wanted to discuss?