One of my favourite K-Drama ever.
Marriage Not Dating is basically a pure rom-com (yes, there are a couple of sad moments, but only towards the end and they get solved very quickly), which is great.
The acting is very good. The plot, though simple, will engage you thanks to its peculiar way to develop (each episode begins with a certain scene that will lead you to believe into something, but as the episode unfold it will turn out to be something entirely different), and it will make you laugh out loud on many occasions.
Considering it's been filmed in 2014, I found surprising that it also shows real physical interactions between two adults, making them act according to their age.
I personally loved the OST, too.
100% recommended!