I've already seen lot of k-dramas, but I admit that this one was special, really different from other dramas. It talks about a earthquake in Seoul and at the same time it doesn't. It's much more than that. It's about people, normal people and how they would react if a disaster would happen.
At the beginning I wasn't sure if I would like it, because I couldn't imagine how they were going to deal with the result of a earthquake for 20 episodes, but at the end I liked it. It's not perfect, there are lots of flaws, but it's ok. Nevertheless, it could have been better with 15 episodes or less, not 20.
Story: I liked the fact that character's behavior, facing a big disaster, is completely different from any american show, where everybody is nice and have a huge heart to help others (and at the same time it's so unrealistic...). Always there will be good people and bad people, and theirs qualities (good or bad) come to light even more in difficult times as a earthquake, and this is something we can clearly see in D-Day. In this drama, people it is what it is.
On the other hand, this drama is a roller coaster of emotions. One moment you are literally crying your eyes out of sadness and a minute later you are mad at the director and you would like a building to fell upon him and karma to do his job.
Acting: I love the main leads... the rest were ok too. At the beginning I couldn't stand Dr. Han Woo Jin, but I think his character gets better at the end. The biggest flaw is the director... it seems as at the end he would be forgiven for all the things he did... I suppose for him and the politician karma does not always works.
Music: the 3 main songs are nice (Memories, the Day, and Let you know).
Rewatch value: perhaps some part of the drama, but not everything.