Many fantasy novels - 'Lord of the Rings', for instance, or 'Lavondyss' by Robert Holdstock - are beautifully written. Geoff Ryman's 'The Child Garden' is exquisite and utterly beguiling. Mervyn Peake's 'Gormenghast' trilogy is an astonishing piece of multi-faceted storytelling. So quality of writing does not condemn the genre.
