Hufflepuff wants to help the world
Gryffindor wants to save the world
Ravenclaw wants to know the world
Slytherin wants to rule the world
I will be deeply dissapointed if Rowling does not get around to the issue of inter-house alliances. The nature of the system she has built is such that any house, standing alone, must destroy itself. They are each too concentrated on one area. Hufflepuff would disintegrate into obscurity, their contributions lost for lack of a forceful advocate. Gryffindor would be wiped out by attrition as they leapt, lemming-like, over tall cliffs without looking first. Ravenclaw would withdraw from the world, their findings never aired because none of them could be bothered to stop long enough to inform anyone else. Slytherin would turn on each other, their thirst to exceed eventually resulting in a single survivor who would die of boredom.
Rowling has been compared to both C.S. Lewis and to J.R.R. Tolkien. Stylystically speaking she does sound rather like Lewis, though without the blunt-instrument-like use of religious allegory. The internal consistency of her world resembles that of Tolkien's Middle Earth, though it signally lacks the mind blowing depth of detail (to be sure, Tolkien took a lot longer and was not busy raising a child alone). The human archetypes she employs do draw heavily on Tolkien's, though she leans toward the comedic where he favored the epic/heroic.
That said, the author she most reminds me of is Charles Dickens, who also favored the use of caricature for all but his core characters to highlight his treatment of moral issues. Personally, I find this annoyingly heavy handed and much favor William Thackeray's satiric use of caricature (see Vanity Fair for a lovely example).
For purposes of meditation on the nature of categories, I divide them thus:
Consistency--a bit on the runny side.
It really doesn't surprise me that so many fans immediately took to writing in the Potterverse. There are so many glaring inconsistencies to be rationalized, it was probably inevitable. Consider these examples from the first books alone.
Snape behaves in a childish and immature manner (eg, deducting points for Hermione's being "an insufferable know-it-all", refusing to listen to the truth about Black). He expresses himself in the manner of a child, and a bratty one at that. He lets his emotions run away with him to an overwhelming extent. This is not the behavior of a competent spy, and yet we are supposed to believe that he survived as a double agent among the Death Eaters.
The Dursleys are extremely abusive toward Harry, both physically and emotionally, but Harry shows no reaction to this at all. That sort of treatment would not, realistically, produce that sort of child. Many fans have taken up the gauntlet of this particular inconsistency, probably because it offers such outstanding fodder for hurt-comfort stories.
Dumbledore is supposed to be a good man and a role model, yet he acts in some extremely cruel ways. Consider the underhandedness at the end of Philospher's Stone. Everyone is at the feast, Slytherin's decorations are up, expectations are high, and Dumbledore takes the prize away from Slytherin in public and by means of a rigged award of points at the last minute. That careless humiliation matches anything Snape manages to do to Gryffindor students with malice aforethought.
About the issue of rules, which seems to exercise some parents greatly.
As far as I can parse it, the basic equation of these books runs thus:
Rules are made to keep people safe. Adventures are not safe. Therefore, in order to have adventures, people must break the rules.
I fail to see what is objectionable about this manifestly true statement.
About the issue of Christianity, which seems to exercise some Christians greatly.
It is not possible for Rowling's writing to be anti-Christian, because she never so much as brushes up against the subject of religion in any form. We do not see any character practising Christianity or Satanism or anything else. The Dursleys might be Buddhists or Anglicans or rabid Atheists for all the books tell us to the contrary. The same holds true for the Weaslys and the Malfoys. I suppose a Christian might manage to be offended that Rowling doesn't mention the subject, but the individual in question had best be prepared to look silly.
As for the magic, it has far less to do with witchcraft, either historical or imaginary, than with alchemy. The title of the first book was a major tip-off, though I suppose I can't entirely blame Statesiders for not catching it right off when the publisher altered the title in such an asinine fashion. It does not surprise me that the evangelical hysterics in this country have remained ignorant of this detail, as that seems to be their ground state of existence. No one else has any excuse; this information is readily available to anyone who takes the trouble to look it up.
In the short form, alchemy does not deal with gods of any stripe and never has except in extremely abstract and spiritually general terms. Alchemy is concerned with complex mechanical interactions, thus the concern with proper pronunciation, precise movement and correct components, to say nothing of accurate notes. The fact that the contents were mistaken does not invalidate the form--alchemical method was what became scientific method. In fact, now I consider it, when one gets down to the level of quantum interaction and the observer effect it just might matter whether or not there is a bird on the roof at the time of an experiment, and which way it's facing. Perhaps the content wasn't as wrong as all that.
At any rate, as Alan Jacobs has noted in an excellent essay on the subject of Rowling's magic, Rowling has simply created a world in which alchemy worked. She offers no reflections on religion at all. Magic does not equal religion in her books, but rather science.
I do not, for one instant, expect that this will exercise the evangelical hysterics any less. They are exactly the sort of people who wanted to hang Gallileo for having the unmitigated nerve to say that the earth (home of Man, clearly God's greatest creation, don't you know) was not the center of the universe. Any form of instrumentality that does not clearly owe its origins to Jehovah exercises them, because it points up in precise degree the miniscule amount of influence their chosen prop and hobbyhorse has on the world when humans choose to look elsewhere.
Fandom would be well served to do its research a little better, too. Rowling draws on a number of folkloric sources for her non-human characters, and knowing what they are makes the issue of how she deals with them more comprehensible. Take house elves, for instance, who clearly owe their antecedents to brownies. One is never supposed to thank a brownie for the chores it does for one. This point, which Rowling has carried over though with her own spin, makes Hermione's desire to liberate the house elves more complicated, raising shades of colonialism and suchlike to go along with the questions of abusive control systems and fear-based politics.