Very slick production, great CGI which does NOT overwhelm either acting or plot (I find in a lot of western films it does both - it's a default for poor writing). Mostly, here, it was very unobtrusive, and used only where needed..
Acting as always very impressive - the star prize going to Kim Byung Chul, who just EATS up the role of Sigma, and has some seconds, then dessert..
Well written up to a point ie, where a character is more than just a goon with a gun, they are reasonably well put together, within the frame of this drama..
However, the plot depends on multiple time slips and flashbacks - I gave up trying to follow it, because it made no sense at all and was just too confusing. It was never so confusing I wanted to give up, though, and that says something for the writing and all the rest. But I found it ridiculously over-plotted. It was as if they were spinning it out to 16 eps with too many unnecessary plot twists and flash backs. Including one final one which was completely too many..
Fights were excellent - and Park Shin Hye shone - but there were a few too many for me, and they became predictable and boring - even though very well done!.
And ... the romance. Well this was completely not required for any part of the plot which could have tota;;y managed without it. And I'm sorry to say I saw no chemistry between the characters or the actors. I like a nice snog, but these were pretty work-a-day..
Altogether, an engaging drama - I gave it a 7