Jour J was never intended to be anything more than a vacuous romantic comedy, and I think it does that very well. Reem Kherici (who also directed and co-wrote the film) shines as the protagonist, Juliette, and it's great to see Nicolas Duvauchelle playing something other than a crook or a bent cop (or both).
Maybe I don't expose myself to enough of this kind of comedy, but I found some of the slapstick scenes to be laugh out loud funny. Notably (and don't worry, these are not spoilers): the wedding scene at the beginning, the prospective bride's father slamming open the window shutters of his coastal home, and the dog chasing its ball at the wedding planner's office. You'll know exactly why I singled out these scenes once you've seen the film.
It's just a shame that one of the writers had to taint everyone involved with glaring plagiarism. The infringing content only represents a tiny portion of the film, but it's hard to believe a production can reach completion without someone noticing. Perhaps it's time Mandarin Cinéma introduced better checks and balances to prevent the same thing happening again - certainly considering it happened with another of their films: Pattaya. The same writer was responsible too!