I highly recommend you to keep aside all your negative ideas of k dramas and watch this show - this isn't just a good Korean show, it's a GOOD SHOW IN GENERAL!
I confess, I initially started watching this show solely because I loved Ji Chang Wook. But it took just 2 episodes for me to get completely sucked in.
This show is so beautifully made - the characters are solid and well developed, with proper back stories and logical, reasonable attitudes. I usually do not like bubbly, naive, dainty female characters but this female lead truly blew me away. Her weird dancing and singing, her optimism, her sense of rationality in the face of adversities - all of this make her a lovable, strong female lead. She can't fight, and needs protection - but NOT because she needs a guy to protect her all the time, but because it's simply illogical to fight when you don't know how to fight.
The male lead is jaw droppingly charming, and Ji Chang Wook offers a stellar performance; he handles the transitions between the character of a fighter and a weak commoner effortlessly.
I think the character that stood out for me was Ms Jo, the female hacker. I love how bizarre, blunt and brutal she was - unapologetically herself.
The best thing about this show is the fact that it has the least amount of the typical TV show cliches, and the romance is just the right amount - enough to make you want more of it, but not overhshadow the plot. The characters are consistent and develop well throughout the course of the show. The mystery itself is super intriguing. The soundtrack is quite strange at times, but you'll get used to it.