I actually quite enjoyed this drama, though I can see why some people didn't. It's like they were trying for something but didn't quite get there, and there were a few moments when I wondered why I was carrying one with this - then something would happen and I'd change my mind.
I loved Joo Won and his character, and though I did get annoyed at Kang Hee's character a lot, I thought she played it well - it was a story problem more than an actress problem.
The story line with her parents was silly and unnecessary, though it did provide comedy. The brother annoyed me.
His parents got just as annoying at times too.
Overall, I think the casting was good, but the story had some major issues, it dragged too much in places, (there was like 3 episodes where it felt like nothing had changed) and felt rushed in other places. Also, the ending could have been so much better.
Not the drama I was expecting, or thought it would be from the start, but not bad, and I wouldn't say not to watch, just don't expect a masterpiece.