Thank you, blackbeanie, for your very thoughtful and apposite comments. Together with MT's review, they chime with my own feelings about the film.

I really loved the movie for several reasons. The first one being the fact that the story stayed true to the book, which isn't evident considered its unusual ending.
The setting and costumes were a joy to watch, the colours were rich and warm. In the cabaret scenes you could easily imagine Henri Toulouse-Lautrec sitting there and observe the dansers.
Though Uma, Christina and Kristin were very well cast for their roles, Bel ami is all about Georges Duroy and his way to glory by bedding women of influential men. In the book, Georges is a complex character who at first isn't really aware of the effect he has on women. A bit awkward in the beginning he learns to use his 'talent' to seduce the rich ladies and climbs the social ladder. He uses and manipulates people but at his turn is being used and manipulated by the same people.
Vulnerable or ruthless, seducing or rejecting, naive or calculating... Georges possesses all these qualities and use them for his own profit.
Georges Duroy isn't a dyed in the wool charmer, he's frustrated and eager to become rich and powerful. His relationships with the ladies is a way to get there, the most easy way for him.
Robert Pattinson nailed his character and those who have read the book know that (experts of Maupassant's work have praised the actor).
He rehearsed for weeks with Donnellan and Ormerod so I'm sure the Georges we see on screen is the Georges the directors wanted.