Simplistic Reviews’s review published on Letterboxd :
For all it's graphic and misogynic violence, "I Saw the Devil" is one of the greatest revenge and horror films in the last decade.
It's a brutal film that takes the viewer on ride that they might not see coming and flips your moral compass more times than you'll want.
Who really is the bad guy here? That thin line between good and evil is tested more times that you'll believe. It's a harrowing, but excellent, exercise in suspense and tension.