The series as a whole is not brilliant or a genuine masterpiece, but I think it's fair to say it's very good. And yes, one reason why it's so good is the masterful way in which Rowling let the series grow with the readers. The first book is a children's book, better than average but nothing really spectacular, you're quite right.

I also certainly agree that the hype helped, it always does. But hypes also tend to have the opposite effect - that they lead other people to think disdainfully about the book or series without even having read it. Some people seem to think that a book or series hyped to such a degree can't ever be good. And that was what Tim was talking about.