Roger Vadim became known for soft-core-ish movies as well as really hot wives, but in the 60s he was most commonly found adapting the classics. It makes sense when Dangerous Liasions had been his biggest hit - he followed it up with La Ronde and here he has a go at Zola.
The movie is a vehicle for Jane Fonda, who became his wife shortly before filming. Critics distracted by her disrobing did not always appreciate what a first rate performance she gives - yes she's sexy, and goes topless in the sex scenes (which happen around the middle mark and that's it), but she also gets to play the gamut of emotions: flirty, scared, lustful, passionate, concerned and, in the end, devastated. It's a performance that would have been beyond Deneuve and probably Bardot (though I think the latter was an under-rated actor).
Her French is pretty good too - at least, it was to my untrained ears. She wears a variety of different outfits and Vadim knows how to make her come across well on screen. (Though I admit at times his direction felt a little "over pervy".)
Michel Piccoli was born to play a wealthy cuckold (you might recognise him from films like Belle de Jour). Peter McEnery is alright as the lover - he's not in Fonda's league as an actor, or as a charismatic presence, but he does. No one else has much of a role though the cast also includes Tina Aumont, daughter of Maria Montez, as McEnery's girlfriend.
I felt Vadim's direction was fairly effective - occasionally flashy to flashy's sake, and some bits felt included just for the critics (there's this thematic thing about Asia going on, with McEnery dressing up as Genghis Khan in one scene, and meeting some Chinese in another.)
Story wise it dragged every now and then but the ending was effective.