A third area to consider (after magic and worldview) in evaluating the merits and demerits of the Harry Potter novels and movies is the area of ethics. Do the Harry Potter novels communicate a biblical view of ethical and moral issues, where that which is virtuous and good is found praise-worthy, while that which is wicked and evil is found blame-worthy?
This question isn't as easy as we might first think, if you start from a God-centered foundation in defining ethics. As Jonathan Edwards demonstrated in his masterful book The Nature of True Virtue, virtue - in its essence - is love for being in general, and virtue can only be measured in proportion to the being(s) loved. Thus it is more virtuous for one to love his family than himself, and more virtuous still for one to love his fellow-man beyond even his family. But, Edwards argued, if God is infinite and eternal being, then it is conceivable that a person could actually show "love" for all of humanity and yet do so irrespective of God who is the greatest being, so that at the end of the day, their love for humanity was not truly virtuous at its essence because it neglected the greatest being in the Universe. Of course that is pretty nuanced, I know. But really, it is just the fleshing out of the first and greatest commandment, which is the foundation of all true ethics: "you shall love the Lord your God with all your heart, soul, mind, and strength." And from this vantage point, there is no doubt that Harry Potter (along with The Lord of the Rings and much other literature beside, for that matter) fall far below the biblical standards of true virtue.
But with that said, we can still ask whether there is even the shell of Christian ethics within Harry Potter, i.e. an extolling of virtues and positive character traits which are extolled in Scripture and the condemning of vices and negative character traits which are condemned in Scripture. And to this, I would have to say that Harry Potter is a mixed bag.
There certainly are many wonderful "virtues" extolled in the Potter novels. Courage. Loyalty. Friendship. Self-sacrifice. (Harry is an especially good example here, as almost every book has him risking his life to save the lives of others). And there are some serious evils which are specifically targeted, most notably racial prejudice (played out in the sub-plots involving prejudicial plots to kill muggles and mud-bloods, i.e. non-magical people and magical people born into non-magical families, respectively) and social and economic snobbery (played out in the sub-plot involving Harry's best friend Ron Weasley, who comes from an extremely poor wizarding family).
But on the other hand, there are some pretty obvious moral evils that get dismissed out of hand - such as dishonesty and anger. Harry Potter and his friends lie frequently - to their superiors, their enemies, and even to one another. Along with dishonesty, Harry's character is often shown to be angry and sullen, sometimes even vindictive - at least when relating to his "enemies" in the books (and not just Voldemort - I have in mind Harry's vengeful attitude towards his nasty relatives, the Dursleys, and his constant ill-will towards his arch-enemy at school, Draco Malfoy). The rivalry between school houses looks a lot like the kind of cliquishness that we want our children to avoid, yet is so common among teens and preteens. The books also bleed a fair bit of moral relativism, with the end often justifying the means. The head-master of the school, Professor Dumbledore, although consistently portrayed as a kind, understanding, wise and powerful wizard, almost always ignores Harry and his friend's frequent rule-breaking. Lesser evils, but still problematic - especially for children - include the occasional use of scatalogical and mildly sexual humor and bad language (both of which get exaggerated in the movies) by both children and adults, even adults that are presented as role models.
To be honest, these are the issues that give me the most pause when thinking about children reading these books. My kids aren't old enough to read yet, but when they are, I don't want them reading books where the protagonists get away with dishonesty or vindictive behavior. Much better in this regard are The Chronicles of Narnia where the nasty attitudes of the children in these books always lead to dour consequences from which they must be redeemed. For example, Eustace's laziness, selfishness, and greed eventually turn him into a dragon and he is only "undragoned" when Aslan strips away the layers of scales and allows Eustace to bathe in a mountain pool (The Voyage of the Dawn-Treader). I don't know about you, but that looks a lot like new birth to me. Unfortunately, that kind of portrayal of the negative consequences of sin and the need for redemption is rare, maybe even non-existent, in Harry Potter.