There has been a small trend lately towards women assassin movies, or CIA movies, and some are great, and some are laughable.
To contrast, we have Columbiana and Haywire. Columbiana is about a girl who becomes an assassin to avenge her parent's murder. She is played by Zoe Saldana, a really lovely actress, who I have enjoyed in other movies, but weighs max 100 pounds and looks like her limbs could snap pretty easily.
In Haywire, you have Gina Carano, a woman who had very little acting experience, and there were moments it showed, but came from a mixed martial arts back ground, was as tall as any of the men in the movie and when she fought them, I absolutely believed she could kick their asses. It was in her movements, her muscle tone, the way she stood. Even when she's running, and jumping in a sequence where she has to escape from the police, there's something in her movement, and her reactions that made her completely believable. I bought that she could run faster than the two police officers chasing her down.
I can suspend disbelief for a while if the movie is good enough, but a hundred pound girl kicking the crap out of a guy twice her size - well that's a bit of a stretch.
But I believed it in Serenity, which also had a waifish girl kicking some serious ass, but that's because she'd been given special powers by the corrupt government that turned against her. We see this a lot in urban fantasy and paranormal YA, young, slender girl with special powers and if it's done right, I believe it.
But once I start to question whether she really can do that, then I'm out and I can rarely get back in. It's what I liked about the Hunger Games movie. Jennifer Lawrence looked like she could run, and climb trees, and fight her way out of trouble. She made it believable. A tinier actress would not have. And I know the movie got some criticism, for casting an actress some believed was physically too large to play Katniss, as she's described as small and underfed in the book.
We see enough small and underfed on the large screen already. I'd rather see someone believable, rather than stick to the exact descriptions of the book.