The latest Harry Potter book is less fun, but more momentus and still genius

The seventh and final volume of the Harry Potter stories has its faults, like all the others, but it's worth pondering J.K. Rowling's extraordinary accomplishment.

What kind of writer has children standing for hours in the rain waiting for the chance to buy her book?

Scroll down for more

An extraordinary, once-in-a-generation storyteller, that's what.

C.S. Lewis's praise for Tolkien's book The Hobbit comes to mind. Tolkien, he said, had written about a world that seemed always to have existed.

That's what J.K. Rowling has done. She seems not so much to have created the world of magic, of Hogwarts, as to have drawn it from life.

Children have an unerring instinct for artifice and artificiality - this story and these characters have the inescapable quality that the author seems as convinced of their reality as the reader.

This book, however, departs radically from earlier volumes in the series - to my mind the better ones.

It's no longer a boarding-school story. Instead, it's the story of a quest, of a last battle.

And so the cycle of the school year isn't the framework for this book as it was for the earlier ones.

Instead we're in a different sort of narrative, the battle of good against evil, Harry against Voldemort, a mini-Gotterdammerung. More momentous, less fun.

And, for whole stretches of the story, it is just the three friends against the enemy and for some of it, only two of them.

But by the end some of the other creatures in this richly populated world come into their own - goblins, the elves and, all too briefly, the giants.

There's much less of the humour and the comic aspects of the earlier volumes.

There was endless scope for fun with variations on Care of Magical Beasts classes, on the hideous things that could happen with potions.

But here they're absent altogether. You also lose the succession of satirical minor characters who enlivened the previous books, such as the celebrity wizard Gilderoy Lockhart.

However, this book has something else, a more nuanced depiction of good and evil.

Previously the inexorable villainy of the villains could get monotonous - the notion that nothing good could come out of Slytherin - when we all know that people are rarely so obliging as to be unremittingly bad.

Scroll down for more

There are welcome redemptive elements in this story, one quite unexpected. I'm trying really hard in all this not to give away the plot.

Yet this final volume deals to an even greater extent than before with the author's conviction that death is not the worst thing in the world. J.K. Rowling is profoundly, subliminally Christian in her way.

These are moral books. As in fairy stories, the characters can draw on magical powers and extraordinary weapons but the human virtues of courage and kindness are what matter in the end.

The books are a celebration of friendship, which is precisely why children relate to them so strongly.

Indeed sometimes the author's didacticism is all too evident - the attempts by the Voldemort side to establish a register of Mudbloods and to discourage marriage between pure-blooded wizards and those of impure and mixed ancestry have very obvious parallels in history.

If you don't already love J.K. Rowling's creation, her fertility of invention, her extraordinarily various world of magic, well, you won't care for this book. The prose is vivid but hardly elegant.

For the rest of us, this is - alas - the last opportunity to hail a narrator of genius.