Story
The idea of the story is integrating a game universe and real universe, which somehow weirdly unique.
The story began with a jaw dropping starts. The story progresses steady but too slow. I really love the core story, but the tempo kills the excitement of watching this.
The problem is that there were too many unnecessary details and time shifts to explain minor incidents that happened before rather than explaining what will happen and what happened with the core story.
Acting
Hyun Bin potrays Jin Woo perfectly. The suffer is so real and I am amazed how great he was potraying this character.
On the other hand, Park Shin Hye started awkwardly. Jung Hee Ju seems to be so awkward and out of places. But it started to get better as the story progress.
The other cast did their job great, especially the "bugs".
The chemistry between the leads is great, but not the best.
Ost
The only great ost is Is You by Ailee. The rest are average.