Okay,
A lot of people slept on this drama because the writer is a complete nut that is infamously known for wack plots and nepotism. But, this easily in my top 20 and one of the 10 I recommend for anyone dipping their toe in the kdrama world for the first time.
Bad stuff first:
Slow start. Give it the necessary 8-10 for the real fun to start.
There's a F-ing ghost and not a good one, like why?.... The writer, that's why.
Dumb af birth secret you realize you don't care about and then they give you another one.
Sung Hoon's acting, most are more than a little green be he stands out as the worst in the beginning.
Eeyore gets a hairdo and it ain't pretty.
Her other choice of ...~cough~ partner...~gross~.

The good stuff:
Sung Hoon takes a shower.
Chock full of madness to make you yell at the screen and tell off the jerk of a male lead who really gets pulled through the wringer, deservedly so.
Sung Hoon takes his shirt off and starts yelling about how much he loves you and wrong for everything.
The male lead actually shows growth as a character without just waking up one day with a change of heart.
Sung Hoon crashes your Skank-wedding, sorry "Courtesan-Wedding"
The lead female isn't a doormat either.
Sung Hoon is all Boo-hoo at your feet begging you to take him back.

Rewatch factor: High.
I have found myself rewatching this one when I'm in a drama slump or I need to wash the sting of a disappointing drama from my mind. So at least 5 times that I've watched this one.