Among other things, King understands, and with great charity, the difficulty inherent in reviewing books for a daily paper:
Due to the Kremlin-like secrecy surrounding the books, all reviews since 2000 or so have been strictly shoot-from-the-lip. The reviewers themselves were often great — Ms. Kakutani ain't exactly chopped liver — but the very popularity of the books has often undone even the best intentions of the best critical writers. In their hurry to churn out column inches, and thus remain members of good standing in the Church of What's Happening Now, very few of the Potter reviewers have said anything worth remembering. Most of this microwaved critical mush sees Harry — not to mention his friends and his adventures — in only two ways: sociologically (''Harry Potter: Boon or Childhood Disease?'') or economically (''Harry Potter and the Chamber of Discount Pricing''). They take a perfunctory wave at things like plot and language, but do little more...and really, how can they? When you have only four days to read a 750-page book, then write an 1,100-word review on it, how much time do you have to really enjoy the book? To think about the book? Jo Rowling set out a sumptuous seven-course meal, carefully prepared, beautifully cooked, and lovingly served out. The kids and adults who fell in love with the series (I among them) savored every mouthful, from the appetizer (Sorcerer's Stone) to the dessert (the gorgeous epilogue of Deathly Hallows). Most reviewers, on the other hand, bolted everything down, then obligingly puked it back up half-digested on the book pages of their respective newspapers.
On the question of JKR's actual writing:
Talent is never static, it's always growing or dying, and the short form on Rowling is this: She was far better than R.L. Stine (an adequate but flavorless writer) when she started, but by the time she penned the final line of Deathly Hallows (''All was well.''), she had become one of the finer stylists in her native country — not as good as Ian McEwan or Ruth Rendell (at least not yet), but easily the peer of Beryl Bainbridge or Martin Amis.