It was hard to rate this, as the first about 20-21 episodes were mediocre and often boring, but starting from around the episode 21 all the way until the drama was good: it held my interest, made me laugh and made me cry. For people who start this and find themselves wanting to give up, I recommend you read the recap for the first episodes and start then watching from the 21st episode, since that's where the most important storyline starts. This is actually were the novel starts, episodes 1-20 are told in flashbacks. I felt the same way with Eternal Love (TMOPB): the best part in the drama starts from the same point as the whole novel.

I have read most of the novel and I can say that this adaptation is very true to the original. Even though some things are changed, most of even the smallest details follow the way they were in the novel.