Excellent character study of Engstrom (Stellan Skarsgard). The viewer is drawn into empathy, confusion, and horror at the character (where the protagonist becomes one more antagonist). The sense of constant tension and a carefully-caged, potentially explosive temperament make Skarsgard's character a must-see.
That said, as a thriller/entertainment (which it probably was not trying to be), the film as a whole felt less than satisfying. I'm sure this was intentional (to subvert audience expectations for a payoff at the end), but it felt much more character-driven (seeing into the deteriorating mind of the character) than action/plot-driven. Of course, when the character is played by Skarsgard, this isn't a problem. 7/10
That said, as a thriller/entertainment (which it probably was not trying to be), the film as a whole felt less than satisfying. I'm sure this was intentional (to subvert audience expectations for a payoff at the end), but it felt much more character-driven (seeing into the deteriorating mind of the character) than action/plot-driven. Of course, when the character is played by Skarsgard, this isn't a problem. 7/10