I actually watched Bel Ami a long, long time ago when it was first released in the UK, but I rewatched it today in prep for university interviews. The first time I watched it, I thought it was an excellent film, albeit with some moments with dodgy acting and raunchy sex scenes. After a while; however, I began to think that it really wasn't a very good film at all and that I had simply been caught up in the moment. Now, after watching it for the second time, I'm back to thinking that it's not that bad a film at all.
Bel Ami is an adaption of the novel of the same title by Guy de Maupassant. I can't say whether the film sticks to the original story or not, but with most films that answer is usually no. Bel Ami follows the story of George Duroy and his rise to power in Paris by manipulating the wives of the most influential men in the city.
All in all, I suppose I would recomend this film because it's a really good story; however, if you're watching it on the merit of Robert Pattinson's acting then you will sorely disappointed. Watch this film for the women, not for the men, as ultimately they are they most powerful women in this film.