The Wilis of Giselle were partly based on the rusalki of Slavic myth, elemental river maidens as dangerous as they were beautiful. Dvořák has invested his otherworldly heroine, Rusalka, with sweetness, but her thrilling kiss is still deadly. This production of the shimmering opera has a classy director in David McVicar, and an excellent cast with Sondra Radvanovsky in the lead. —L.J.