It is really like that, you dig Korean action drama or you don't. If you do, you may actually enjoy it quite a bit. There is not much logic here, true, and reasons for anything are, at the very best, faintly perceptible. But is not really the point. You have plenty of crazy action, sometimes funny, sometimes silly, occasionally a bit sad. What else do you need? Rain (Ninja Assassin) is really good. He steps into the character with ease, playing a rouge, funny, silly and sometimes surprisingly serious PI, in the very best tradition of the original Lupin III manga series. Lee Na-young (Ruler of Your Own World) managed to make her character believable and, trust me, it was not an easy task - see the part about reasons above... :) The supportive crew is really good - Henney being sort of perfect for his character (a dubious honor, but true), and Lee Jung-jin and Yoon Jin-seo complementing each other perfectly. Special prize should go to Seong Dong-il, playing Namkamura Hwang, he is The Nakamura. ;)
Martial arts choreography is impressive, although a little bit too smooth for my taste. Korean directors seem to prefer a dance-like quality in the fighting scenes and it shows - as usual. Yet I cannot honestly say it is some kind of a setback, just part of K-drama experience. ;) I got to really appreciate Lee Na-young performance in fighting scenes. She is not an action heroin and it's well worth seeing the special episode ("21") just to see how much work did she put to make it look like it does.
Good camera work, in some scenes bordering on excellent, music fits the rhythm of action - sometimes vice versa. Seriously, what more could you want? And yes, to be honest, I would say a solid 6 out of 10, but the fact is, I just feel some guys tend to give bad score simply because they don't like K-action drama. So - bear with me and enjoy! :)