I once read someone opining that the worst thing that can happen to a national cinema is for it to become a genre. I don't think there's any real danger of that happening to South Korean film (there are too many idiosyncratic voices working in the industry) but it's fair to say that even a filmgoer with only a passing knowledge of the nation's films could construct a bingo card for the typical commercial movie. A Hard Day would probably allow you to fill out that bingo card in under 30 minutes. All the boxes are covered: Wild tonal shifts, brutal violence and a soupçon of social commentary crop up relatively early.
Fortunately A Hard Day is a fairly accomplished version of Commercial South Korean Movie. It's stylishly, albeit somewhat anonymously, directed in a way that only occasionally starts to grate (check those dutch angles!) and is blessedly free of the super fast continuity editing that plagues the films of Na Hong-jin. It also does an excellent job of placing its protagonist, sympathetic dirty cop Go Geon-soo, in memorably tense and funny predicaments. It never really tops an early set piece involving a child's toy, a dead body, balloons and a shoe lace but that's to be expected.
A Hard Day does occasionally drift into excess. The score can best a described as overbearing and the climax is overextended (check your bingo card), but for the most part it zips along and it will provide an excellent exemplar of what Korean film in the 00s was like.