I got so excited when I first heard about this movie and it DID NOT disappoint! Casting is absolutely perfect: Park Seo Joon and Kang Ha Neul have great chemistry and they make an amazing comedy duo. Their friendship seems completely natural and they are hilarious together (separately too).

Writer / director Kim Joo-Hwan did an excellent job at mixing comedy with a dark storyline. It could have been a total mess, but everything flows really well and all the aspects of the story fit perfectly together.
I also thought the fight scenes were really well choreographed, more realistic than those I've seen in other action dramas / movies.

I don't have too much to add, as I liked everything about this movie: it's an easy watch that will make you laugh and I highly recommend it!

Oh! Wait... One thing I could add: lots of Park Seo Joon shirtless scenes. That's it.