Beckinsale is a soft, elegant beauty. Gardner was a hard, ruthless beauty. But as someone said, her specialty was "she makes you think about sex - and how!"
Her recent biographer sums up her appeal excellently:
She was who she was: Ava Gardner. Actress, love goddess. Resident of London, Madrid, Hollywood, and Grabtown. She liked jazz and driving too fast and nights that went on forever. She loved gin and dogs and four-letter words and Frank Sinatra. Once upon a time she was thought to be the most beautiful woman in the world. She had luminescent white skin, eyes like Andean emeralds, eminent cheekbones, a wide, sensuous crescent mouth, a sleek, strong body that moved with a feline insolence, and a dancer's grace. She played temptresses, adventurers, restless women, in the movies and in private life. On the silver screen she conveyed a powerful image of dark desirability. To see her in the flesh was said to have made the blood race, the hair on the arms stand up. To know her more intimately was to surrender to mad passions, to risk all.
An excellent pick for the part would have been someone like Monica Bellucci, Catherine Zeta Jones or Laura Harring with their earthy gypsy looks. Beckinsale with her ethereal beauty is an entirely different type, more suited to a Vivien Leigh. That's why there was much to-do. Of course Blanchett looked nothing like Hepburn, but Gardner's main stock was always her image and looks and people were disappointed when a physically dissimilar actress was cast. It would be like casting Gwynneth Paltrow as Marilyn Monroe. That said, Beckinsale looked quite smashing, as she did in Pearl Harbor - I really wish she'd keep with the dramatic dark hair/pale skin combo instead of the unremarkable brown on brown coloring.