Heath Ledger, starring as the fabled 18th-century Venetian lover, meets his match in a spirited, protofeminist beauty (Sienna Miller). Lasse Hallstrom (Chocolat) directs a sparking screenplay by Jeffrey Hatcher (Stage Beauty) and Kimberly Simi; it starts as a frothy boudoir comedy but evolves into a masquerade by turns sweetly meditative and sharply satirical. Oliver Platt is hilarious as "Il Lardo," the pig-fat merchant engaged to Casanova's ladylove, and Jeremy Irons oozes reptilian malice as a pompous Catholic inquisitor thwarted by a series of increasingly complicated impersonations. Lushly romantic and forgiving of human foibles, this sumptuous production offers pleasures both earthy and ethereal. With Lena Olin and Natalie Dormer. R, 108 min. Century 12 and CineArts 6, Esquire, Landmark's Century Centre.