I watched this for a screenwriting class; it's not the first thing I would recommend to my students, but there's enough here to appreciate. There's no dialogue for the first, maybe, ten minutes; it's a montage of the two kidnappers very elaborately setting up their apartment room where they will hold their victim ransom. The script has enough twists, turns, and raw performances to keep you interested. Because the movie starts out with the two kidnappers and spends most of the time with them, you end up feeling for them at a couple spots (I won't spoil what the reveals are, they actually will take you by surprise). What enhanced my viewing of this immensely was turning on the Saw soundtrack over most of the movie; you should try it to. Like Saw, the majority of the runtime takes place in one room, or here, one house. It's not the most original script ever, but it kept me engaged to a degree where I didn't want to turn it off, and that's high praise from me.

Descent movie, but very predictable.

If you want to see Gemma Arterton naked on a bed this is the movie for you. If you want a story or fair acting, avoid.