I just finished Wizardry and Wild Romance by Michael Moorcock.

Wizardry and Wild Romance is a study of epic fantasy Moorcock wrote back in the 70s and then revised in the 80s. As such, it obviously missed the Harry Potter phenomenon and the resurgence of Tolkien that followed the Lord of the Rings movies, but I think that he wouldn't have liked either of them. From this book, he is fairly dismissive of Tolkien (referring to it as "epic Pooh") and my guess is that he also wouldn't like Rowling's writing. His main criteria seems to be the lyricism of the writing. He brings up a number of other points, but they are all illustrated by samples of writing that are either praised or dismissed based on the writing alone. This is not surprising since he was a leader of the British "New Wave" SF movement, a movement towards more "literary" writing in genre fiction.

I was hoping for more history of the form, and relations between various authors. Instead, this is mainly a critique, and a flawed one, since he does not provide compelling evidence why he considers some authors better than others, just snippets of their work.