I love the chinese original version (watched it twice) and I love this version as well! They really did a great job with this remake and while I constantly compared the cast and characters of both versions in the beginning, I grew to love the korean cast so much I stopped comparing them along the way and only saw them for who they were.
The plot is simply about life as a teenager and everything one has to deal with while growing up - from grades, career choices and friendship to your first love.
And here's the thing some people apparently forget about: During 80% of the show the characters are teenagers so OF COURSE they're going to act impulsive, immature or even mean sometimes. As a teenager you're confronted with emotions you haven't felt before or at least not to that depth and you don't know why you feel that way or how to deal with it so yes, you're gonna do and say things you don't mean. And this is exactly what this show is about: growing up with all of your firsts and mistakes you make along the way!
I bet none of you were perfect as teenagers either so don't be too hard on the characters and their behavior along the way.
Instead, enjoy this light drama and feel yourself thrown back to your teenage/high school years.