It's a bit refreshing to see a romance drama not relying on super powers, ghosts, supernatural events, vampires and the like to add to the love story. And since this one here is quite simple, that's exactly what makes it - in my opinion -  a little bit special.    
I had a really good time trying to figure out what would come next in each episode : since the setting of the show is close to our every day life, you don't feel the distance others K-dramas tend to put on their viewers as unnatural forces get involved. While for some shows there's a real "plus-value" to get 'bigger than life', I'm sure you've also experienced some amazing train wrecks along the rail ^^
Here's a tv-drama with a simple setting, and some colorful characters trying to get along and getting hurt, loved, hated and everything in between in the process.
This kind of show is perfect to renew some love for K-dramas (if it is ever needed). If you're feeling a bit bored, this drama is offering a nice change of pace.
I can only recommand this show since it came at the right moment for me, maybe it could do the same for you ?
Then your only conclusion will be, hopefully, the same : that was a good show, I had a good time and I hope others will have, too, watching "Marriage, Not Dating".