If your prime reaction to a film is one of disappointment there are usually some good reasons. My principal response to this version of a great and well-known story is one of irritation. The overblown theatrical format of the film gets in the way of character and dramatic development, to the point where you're aware of a director proclaiming "aren't we clever with the way we're staging this?" instead of admiring the straightforward and competent telling of a story. I'm not saying all films have to be constructed in a conventional manner, but when the form overtakes the substance something has gone wrong.
Aaron Taylor-Johnson as Count Vronsky is a piece of serious miscasting. Instead of looking like a great lover and sure temptation for wavering Anna,he looks like some feeble dandy with his foppish shock of dyed curly blonde hair which makes him look quite ridiculous. How on earth Anna could fall for such a creepy-looking guy is beyond most viewers I would submit.
Keira Knightley does the best she can, despite looking most of the time like she's attending a fashion shoot. The character of Anna requires portrayal of a tragic life which she doesn't quite achieve. However, the whole film fails to convey the grandeur of Tolstoy's vision, so she's let off the hook by the film's general levity and lack of substance.
