Fantasy is in style right now. “Narnia” fans are jonesing for the sequel next May (did you see that trailer?). “Harry Potter” can’t be stopped. The “Lord of the Rings” franchise earned and deserved all its awards, and “The Hobbit” is a fierce issue on every film forum on the Web. All are popular by economic demand, but often passable and forgettable by design. The problem with fantasy is that it’s difficult to film. Who doesn’t think 1988’s “Willow” is a little hilarious? For the level-headed filmgoer, magic is kids’ stuff without the right execution. It takes great deal to buy into witches, wizards and faraway places outside the norm. Sure, teen magic and epic journeys are familiar and affecting as an extension of the usual tropes. But anthropomorphized, battling polar bears? That’s just crazy. Fantasy tunes of a more astute ilk