Highly clichéd and the characters are over the top caricatures. I wouldn't say the acting is particularly impressive, neither is the attempt to have 25 year olds playing the parts of teenagers at times. The writers have the actors doing things that are totally unrealistic for the sake of plot and storyline.
The problem I have is the show is trying not to take its self too seriously but at the same time be a touching drama. That's a difficult thing to pull off and was done masterfully in the movie My Sassy Girl but just to prove that is not necessarily an inherent property in Korean productions, this one doesn't succeed too well in that department.
Having said all that, I do actually enjoy it. I feel guilty enjoying it as it is almost as bad as a show called Malibu CA from the late 90's.