It’s a high time for high fantasy. Novels about wizards outsell (and often outshine) the most glittering literary fiction titles; the contemporary romantic hero generally sports a pair of fangs; and even now the five remaining earthlings who haven’t read “The Lord of the Rings” are being hunted down and put to the sword. Yet for all of fantasy’s successes, there remains a chip on the spaulder of the genre. As Michael Agger put it in 2009, reviewing Lev Grossman’s Harry Potter-­influenced novel “The Magicians”: “Perhaps a fantasy novel meant for adults can’t help being a strange mess of effects. . . . Sounds like fun, but aren’t we a little old for this?” And with that, hundreds of years of fantastical writing are reduced to 20-­sided dice, pencil nubs, half-filled Coke cans and the crushing realization that no, your elven rogue’s dagger is not going to be effective against green slime.