This is a good start. It's fresh, spontaneous, funny, entertaining.
The leads: there's tons of chemistry and they look SO good together which is a plus.
Jung So Min is mastering this kind of sassy, strong and energetic girl who is quite witty too. She is like a magnet to the male lead.
Jung Hae In is refreshing because even though it's impossible not to notice his amazing looks, he also has this calm and deep vibe (without being pretentious) that makes him more attractive and interesting.
In regards to the story, despite the premise is simple, I think that may be because the focus is going to be on the characters and their development and pressure to become functional and successful adults in complicated Korean families. Also, the dinamic and pace of the story so far makes it much more enjoyable.
So, everything is promising and makes me think this could be a huge hit.