Why 9/10?
I usually rate romance dramas around 7 or 8 at most. I gave this one an extra point because of its focus on the understanding needed for a couple and how well it was portrayed. From start to finish, this was all about what happens when:
1 - you don't try to put yourself in the other person's shoes,
2 - what happens if you do try,
3 - and what happens if you try too much.

Story:
I liked the parallel with the weather but as I said the most interesting thing in this drama is its psychological aspect.
The secondary couple was fun to watch, I guess that's how producers justified to call it a romantic comedy. But with the main couple, it's a borderline melodrama at times so I agree that the comedy tag had to be removed.

Acting/Cast:
I'm not a big fan of Park Min Young but it's the first time I actually liked her acting. I'm guessing that's because she doesn't smile as much in this drama so it doesn't feel forced. I suppose her character's personnality is closer to her own actual self.
As for Song Kang, it's my first time watching him as a main lead and I quite liked him.

What is this life-lesson you'll learn in this drama ?
Do try to understand how others think and why, but above all don't just assume things and go talk to them to be sure you're right before doing anything stupid.