This show is full of twists and turns. The first episode will grab you up and the second will confuse the caca out of you, but just keep watching as the writer delivers each piece of the puzzle bit by bit. Although, the story was not flawless by any means -- because there are definitely parts that didn't line up by the ending, it was still a crazy ride with interesting characters and a twisty plot that keeps you guessing and surprised until it's over. The episodes started to run pretty long at about an hour and a half, but I'm not even sure when that started. (So I would say that means I wasn't bored at all) I would say that the finale was probably the weakest episode, but that's all I can say without giving anything away. I would also say as a warning, a few episodes in this show may require a strong stomach. Also early episodes may also be better received if you have a bit of an appreciation for dark humor. So I'd only recommend it to those that don't have aversions to those things.
I gave this show an 8 because it did not fail to entertain me and keep me hanging on to watch the mysteries unravel. I just can't bring myself to lower the score any further even with some of the uneven writing.

This was my first time watching Song Seung Heon, and although I've heard some negative things about his acting, I thought he did a great job in this. Having watched Go Ara a couple of times, though, her acting I would say hasn't improved that much - or the character was just not written as well as they could have. I think the writers could have made her a stronger character. Overall the acting was done pretty well for most of the actors. 

I enjoyed the music in this and will probably search out the main song that played.

The rewatch value could go either way. I probably won't rewatch anytime soon just due to the sheer length of this show and for the fact that now I know the plot. However, for some, maybe a rewatch would make seeing the pieces fall into place more enjoyable from the vantage point of knowing the final outcomes.