Reasonably boring show with an underwhelming story for maybe 6-8 hours that moves at an often-glacial pace. This whole thing could have easily been cut by 10 hours. The backstory that keeps getting onion-peeled and flashback-dissected over and over again is simply boring and uneventful, and the way the flashbacks always add a few more seconds onto a scene the viewer is not even invested in gets really annoying really fast.

Every actor plays their role in the same way they always do. The romantic chemistry between the leads is about as sizzling as a glacier as well.

Lee Ha Nee is vaguely entertaining I guess. If you can't derive some joy from watching her face muscles, just stay far away from this show.
Lee Sang Yoon just doesn't have a lot of relevance for much of the plot (while being on screen a lot). His performance feels a bit phoned in too, like he is on the verge of being too old to stand in front of a camera.
Kim Chang Wan isn't in danger of doing anything original, but at least he's always pleasant to watch.

Jeon Gook Hwan must have played that role a dozen times.
Na Young Hee isn't as annoying as in other shows where she's the evil chaebol mother/step-mother, but that's really the only good thing to say.
The entire chaebol family bully Mi-na in a way that's merely tiring and repetitive for the viewer.

Bonus mention to the music that's either out of place (what's with the cyber-gaming theme of the intro and some OSTs?) or really boring.