I've read all four and I have to say I'm glad my kids are old enough that I don't have to make a decision re: whether to allow them to read the books; "Goblet of Fire" in particular I thought was very dark, for younger children in particular. PERSONALLY, I liked them; found them to be witty & clever & a marvelous escape. But I do understand some of the concerns of others. And I agree; glad LOTR is what we're about here.:^)
From what I understand Rowlings has stated that it is her intention to increase the "darkness" of the books as the series progresses. Too bad.
-Kevin