I started this because I was intrigued by the leads (I enjoyed both in other dramas) and I watched the CN and K versions.
Story: This is a loose adaptation. The MLs motivation for being a cold fish are different, they spend a good portion of college lying to her parents for no reason and reuniting looks different (No sad bench scene, ML doesn't trick her into proposing, etc).
It's only 18 episodes so things are a bit truncated. I expected that but I think they wouldn't have been so rushed if they had spent less time on the HS arc. I feel this way to a lesser extent about the other versions as well. In every version we only get 2 episodes of them getting back together/working on their relationship. Which is especially odd in an 18 episode show.
The main couple are good together but they don't spend that much of the drama together. Literally, I felt like they had more scenes with the other characters than they did together. Controversial opinion: I think the K drama is the best at showing that the ML likes/loves the FL before the break up/time jump. *Dodges tomatoes*
The CN shines for me in episode 23... Once he actually starts talking about his feelings. And openly returning her devotion. It was the same here. In every version we get that she loves him but none of them do a great job of showing why until the end. I really enjoyed the main couple in the last episode. That is both good (yay for a romance giving romance!) and bad (too few romantic moments in a romantic comedy).
The 2ML is good at providing a foil for the ML. Very in touch with his feelings and very open about his love for the FL. It was weird that he was an Olympic level swimmer yet the ML kept beating him in races. It didn't help the feeling that the ML was good at everything but life, lol.
The second couple also has some changes (he is still sick but that is only one of their issues in this version, the other is his job).

Acting: Dew will get a lot of flack for being flat but HYT was as well in my opinion. One of my biggest complaints about all three versions is that *stares blankly as his GF cries about his inattentiveness* doesn't playout on screen the way it did in the book because we don't get any narration. He could be thinking about his laundry for all we know. They gave us a few voice overs but just a bit more emotion even if it's silent would have helped.
Prim was doing most of the heavy lifting but that is the FL in every version of this. She absolutely sells the "I love this pretty mannequin and I will fight for him". They also gave her pretty good dialogue. Every time I thought she should call him out, she did! Especially, during the break up. He said he was tired and then she said she was too and talked about how she did everything in their relationship! I was like "Yes! He's tired?! Join the club dude, we meet on Saturday night and talk about what a dweeb you are!!!"
If you are here for kisses there aren't many but there were no fish lips. Or that weird thing some Thai dramas have where they look like they are trying to fight with their lips.
The second couple was okay but they didn't have much chemistry.
The parents were mostly okay but the lady playing the MLs mom was so dry. Which was terrible because those were the only scenes in the first 10 episodes where the ML actually said more than 3 words at a time, lol.
Prodution: Pretty good. The sets were nice and the houses actually looked like the characters lived there. As always the dorm rooms were insanely large.
Costumes/Hair/Makeup: The wig is always tragic. SY had short hair so the CN is always a bit better here.
Once the time jump happens, the clothing is pretty good. Except the shoes the FL wears at the 2nd couples wedding. They look crazy with her dress.
OST: I am not the best judge her but all of the songs fit the scenes.

Overall, this was a very okay drama. If you love the CN or are very attached to certain plot points, SKIP THIS and save yourself the annoyance.
If you love the 2nd ML comes because you think he is cute because the FL never really seems into him.

I rated higher than it probably deserves because the ratings seem to be people pissed that it isn't exactly like the CN.