[W]hen you read, it’s your brain that’s generating all that data. That’s hard work. Your brain makes all the props and sets, does the voices and renders all those fancy digital effects. When you read, you’re truly collaborating with the author — it’s not a passive experience; it’s an active one that binds you to the book you’re reading in a way no other medium can. It’s hard. It’s work. And you’re richly rewarded for it.
But when publishers mix reading with other media, the way Pottermore does (or the way that The 39 Clues, another Scholastic creation, does), I find it confusing. Every time I see more of the Potterverse realized in other media, as video or audio or even still images, it undoes the work I did by reading about it. It takes away from the marvelous, handmade Potterverse I’ve got going on in my head and replaces it with something prefabricated. It was prefabricated by a super-talented artist, but still. —Pottermore: Is New J.K. Rowling Website Good for Readers? – TIME.