Nobody wants a painfully slow death: do you want to watch one, even if it's set against the crumbling beauty of Venice? Visconti's '71 adaptation of Thomas Mann's novel is a classic no one dares question, but its study of ageing composer Dirk Bogarde falling in unrequited love with a golden, fey young boy is stately and overwrought, and so enamoured of itself it forgets the audience. Perilously sluggish.