Good, not great. Really nice cinematography. Great job by Benicio. And actually, Brolin killed it; I suspect this is much like his actual personality which would have helped.
I thought the writing of the dialogue and some character interaction was stupid as hell. Blunt's sense of honor was a little to overdone for me. For instance, the 'signing of the affidavit' scene was absurd. With someone pointing a gun in your face, especially an off-the-rail killer like Del Toro, you'd sign that thing without any reservations whatsoever. There'd be ZERO internal struggle. I don't see that as a reality anywhere. It's not like she was signing over someone's life and condemning them to death. Her naivete RE what goes on for these types of jobs was silly as well.
I thought Blunt, though she can act, was wrong for the role. She just doesn't sell it athletically/physically as a female. You need someone more Jennifer Garner-esque physically. Acting-wise, she was good, despite the poor writing of her character mentioned above.