In my opinion, the Japanese version was able to keep the story as they had originally stated for the most part as a romantic comedy because no matter how tense the situation became, there were always elements of comedy added whether it was through dialogue or just something quirky added like the main characters facial expression or exaggerated actions. This is where the Korean version, though extremely close and much more lavishly created than its Japanese counterpart, didn't do so well. In the tough situations, the show became a melodrama of EPIC proportions, with the slow motion falling of tears or fainting. *sigh* see the pics below for what I mean.
Another thing that really bothered me about the Korean version was the fact that the character development was really, REALLY SLOOOWWWW. Ugh and I mean double UGH. It took forever to let the characters develop, which includes stuff like understanding their problems and getting over them and their relationships with each other. I mean it took Goo Jun Pyo about 6 episodes to figure that he was going to fight for and stay with Geum Jan Di, whereas the Japanese version shows this particular conflict come to an end in about 2 and half to three episodes max and moved on to the next conflict. It showed the overall growth of the characters and their conclusion as well as how each resolution impacted the characters. In the Korean version, in my opinion the biggest hurdle that Geum Jan Di overcame was her initial infatuation with Ji Hoo and but other than that, she's shown as the perfect girl with a golden character who doesn't need to change too much. Goo Jun Pyo's character does change very slowly but there is not as much development when compared to Doumiyouji. Doumiyouji's character changes drastically from the beginning to the end of the series which includes him having softer facial expressions and less fights with Makino. The other characters like Ji Hoo and Woo Bin are the most static with very minor changes and not to mention the super clinginess of Ji Hoo is more than just an eyesore (don't get me wrong, my heart aches breaks and cracks for the poor dimwitted guy but MAN UP and freaking MOVE ON) he's just ugh...
Neeways, the only character whose development I enjoyed watching was Ji Young. The Korean version did a great job of showing how his character broke out of it's playboy mold to take charge of his own life and not fall victim to his father's legacy of sleeping around with women. This guy learned from his mistakes and Ga Eul helped him fight his demons. I was thrilled to see them accept each other at the end of the drama when he comes straight to her from the airport. The Japanese version showed that the relationship for Yuki didn't go so well because it was doomed to fail as a one-sided love with no interest on Sojiro's part. They did show an initial attraction but no conclusion except for Sojiro constantly running away from her.
The ending for the Japanese version was my FAVORITE I mean talk about the excellent conclusion to an amazing story considering all the hardships that the characters had been through to get there and there was a sense of accomplishment to it. The wedding was gorgeous and Matsumoto Jun looked great with Inoue Mao. I wish that the Korean version could have brought a more clear ending other than the awkwardness at the beach with Goo Jun Pyo proposing and Ji Hoo with the other two showing up to object at the marriage. Not to mention the lack appropriate emotional expression on Geum Jan Di's face. That was my face plant moment because after all the tears and depression, not to mention the constant breaking up and hooking back up together, all I could get out of me after finishing the series was a sigh. It was more of a "Thank God it's over" rather than "That was such a beautiful ending!" moment.