Entertaining, even if that's almost entirely thanks to Mila Kunis.
'Friends with Benefits' has surprisingly more to it than I would've predicted, it's not just about sex, sex and sex. That does take up large portions of the film admittedly, but there's more heart to it - especially with Justin Timberlake's character.
I like Timberlake (Dylan) as an actor, but this is one of his weaker showings in my opinion. He doesn't give a negative performance and doesn't lower the quality of the film, I just felt this wasn't one of his best.
Kunis (Jamie) is terrific, as usual it seems. Her performance is very enjoyable, she portrays the personality of her character nicely. She definitely keeps things moving, even if Timberlake's role gets more depth.
Woody Harrelson is amusing as Tommy, while Richard Jenkins gives the film a touching side with his role as Mr. Harper. Overall, I reckon this gets most of what it aims to right. I'd say you should give it a view.