This show has a unique and addictive plot, with amazing cinematography and special effects.
I can't give a 10 though, for 2 reasons:

1. The first show, for me, with Lee Jong Suk. At the beginning, I simply thought that I didn't like his acting choices most of the times. However, I saw him in other shows after this one and he grew up on me a lot, as an actor, therefore I guess that the problem lies in the way he's been directed in certain scenes. The same goes for Han Hyo Joo.

2. While absolutely captivating in the beginning, the plot gets quite convoluted towards the final episodes, and not always organically. It's like writers felt the need to make it pointlessly complicated.

Even so, I recommend it because it's something really uncommon to watch.