The Good:
The female lead (Hyeri Lee) is so cute and has a positively radiant smile. You really wanted things to work out for her. Her energy was infectious.
The 2nd female lead (Han-Na Kong) is truly beautiful and her acting deftly navigates the line between being worldly and a bit ignorant. That must be really hard to pull off, but she does it so well - it was a lot of fun to watch! I just loved her expression when she realized she had said something silly or ignorant. I'll look for her as a lead in other dramas.
One of the second male leads, Do-Wan Kim, also really helps make this series work. His character is kind of a dork, but you can't help but love him and root for him.
One thing I did appreciate were the comedic elements. They really kept it fun even when (as noted below) things tended to drag a bit.
The Sub-Optimal
The story dragged a bit in the middle. My wife and I both thought that they could have cut a couple of episodes. For a few episodes it just felt like it wasn't going anywhere, or maybe it went back and forth. It was actually a bit hard to remain invested in the main couple. In fact, I found myself caring more about the second couple (Do-Wan Kim and Han-Na Kang) and rooting for them to get together! :-)
The love triangle. Gad, I hate love triangles. Although I think In-Hyuk Bae's acting was great, and his role was pretty critical to the story, it still annoyed the heck out of me. But that is probably just me and I know lots of folks are into the tension a love triangle brings. It happens All The Time in KDramas, but IRL not too much. There is enough drama in couples' relationships that adding the love triangle element is mostly just a distraction. Oh well...
Overall
I liked the series and was glad I watched it. Parts were very fun and it wrapped up well. But it could have been more tightly written.