It's hard to believe that it is 10 years since the apprentice wizard Harry Potter first appeared in bookshops. Since then JK Rowling's creation has been translated into 65 languages and sold more than 300 million copies around the world, as well as five motion pictures so far, making Rowling herself a billionaire.

At midnight on Friday the franchise comes to an end - although Rowling herself says "never say never" - and many millions of more copies will be sold in the coming weeks. Why is it that a book - an unfashionable medium in the age of cable TV, YouTube and the iPod - has had such an impact?

The internet has had an impact on Harry Potter though, with images of the final edition, Harry Potter and the Deathly Hallows, popping up in cyberspace, despite frantic legal attempts by Harry Potter's publishers. And old-fashioned human error has seen copies of the book sold days before the embargo ends. Two US newspapers, the Baltimore Sun and the New York Times, have already published reviews (although both have been careful not to give the plot twists away).

According to the New York Times review, the Potter series is a bildungsroman worthy of comparison to Charles Dickens, while the world JK Rowling has created is compared in its richness to classics such as Tolkien's Middle Earth. Yet elsewhere Rowling has been fiercely criticised for her writing style, and others have read into her wizard world an unhealthy nostalgia for an England of public schools and quaint villages. Arguments rage about whether or not Harry Potter has encouraged more children to read books, and what the effect has been on the publishing industry.

We continue the debate here on Comment is free with a series of writers giving their own take on aspects of the series, starting with Richard Adams' alternative epilogue about a fortysomething Harry and Hermione. It's all a bit of fun. But what do you think?

Ahead of the publication of the final episode of JK Rowling's Harry Potter series, Cif writers look at Pottermania.