The arrival of Amarantine, currently No. 10 on the Billboard album chart, is a reminder that Enya is one of the savviest operators in the music business and, well, an original. Twenty years ago, no one dreamed that there would be a huge audience for an ethereal female vocalist singing pseudo-classical airs with misty mystical overtones—-and Enya remains the genre's only practitioner. No one has even tried to imitate her.