Definitely good, though only thanks to Marion Cotillard's excellent performance.
The premise is intriguing and features some emotional scenes, there's one with Timur (Timur Magomedgadzhiev) that particularly hit me in the feels out of nowhere; it's not even the most gut-wrenching part of the film, yet it made me feel something the most.
The camera work et al. isn't all that great, the dialogue is especially underwhelming. Perhaps I was noticing it more due to viewing with subtitles, but there's a lot of moments where we see Sandra (Cotillard) retrace the same steps with each individual - it gets repetitive.
Cotillard, though, is top notch. She brings so much emotion and realness with her, nailing every single scene to deserve notable props. Away from the Parisian, there aren't any others to note; they are all fine but I would've loved a more meaty cast.
I'd be rating it a level lower if it wasn't for the lead, who is easily the best thing to come out of 'Two Days, One Night'.