Rowling has reached that peak in her writing where the flaws are seamless.
The story takes it's time, no longer feeling rushed, but remaining easier to read. The characters have matured with the writing, and continue to act as normal characters (though Ron seems to be a bit off putting in this book for me).
This is also the start in the series where everything from the past book collides, that epic moment where the real threat is now real and no longer a random moment of events that are following Harry Potter. Being the book to start that, it's great to see that she no longer rushes the story, allows each moment to unfold at it's own pace.