Consider the popularity of the c-drama original, it would be difficult to not draw some form of comparison. The simple, short answer so that we can get the elephant back to the zoo is that this was a problematic adaptation with a number of issues that made this version less than the sum total.
First of all, the k-drama version was 24 episodes long while the Chinese original has the same episode count but the runtime is twice as long. So the writer-nim had to trim the storyline and subplots to make it fit. They did a ok job most of the time and I definitely recognise some of the key scenes from the original and the show flowed in the right direction. However, there are definitely editing issues. For instance, in ep. 14, the ML of the 2OTP confessed very publicly to his crush but by ep. 15 the show seemed to have forgotten it ever happened. Later on, the OTP met up again after 3 years of separation and he begged her for forgiveness. She hesitated and told him that she needed more time. The scene faded to black and the next scene opened with the ML finding her asleep in his bunkbed in the hospital. They had a good long cuddle in bed afterwards which is quite a leap from "I needed more time".
This level of pruning meant that the show was reduced to a standard school/college romance but the story still spanned 13 years. Unfortunately, some of the nuisances, depth and character growth from the original got left on the cutting room floor.
This long timespan also exposed the biggest problem for this drama. The FL was trying her best to be convincing as a teenage girl in the early part of the show and she made it work a lot of the time but occasionally she would look too mature or tried too hard to act young. She had a much easier time later on when they had aged. A bigger problem was the ML. He is an idol and this was his first acting assignment. He definitely has the looks and can sing and dance but his acting abilities were not up to the more challenging scenes. It was just as well that the role of the ML was basically cold and emotionless but he took that to the next level. Even when he was suppose to be angry or frustrated his expression rarely changed. This presented the opposite problem to the FL, when he was supposed to be in his late twenties (and older), a doctor with years of overseas training, his lack of maturity/gravitas and limited range just didn't sit comfortably with his portrayal.
This lack of emotional range also impacted on the chemistry of the OTP. Not saying that they don't look good together but there was little passion. What skinship there was, was not convincing. Stuff happened but there was nothing to see.
The 2OTP was decent but mostly on rails. While they progressed as expected, there were moments when the show seemed to lost track of their progress and they just bunny hop around their relationship status.
One area that this show did do better was when the OTP met again after their separation. The original seemed abrupt and a bit contrived but this version kept it simpler and felt more organic.
The OST was good and bubbly to match the general rom-com setting.
If you have not seen the original then this is a fluffy, easy to watch school/college romance. If you love the c-drama original then it would be hard for you to give this a high mark.