I really enjoyed this drama but most of the time because of Wootak. I loved this character. I'm a big fan of Jongsuk's work but I have to confess that even though I like his character here, he didn't caught me as much attention as Wootak. He really caught everyone's attention, obviously because of his character, and especially because of Jung Hae In's perfomance.
Speaking of acting, I think everyone was apprehensive when saw Suzy in the cast, but she proved that she could be a good actress. Suzy played her character very well, she did a good.
Well, let's talk about this drama.

Story: (8.5/10)
It's  very interesting. I was intrigued by what was going to happen and why Suzy had those dreams.
I found the story quite different and interesting but, yeah,  had some holes. That's why i didn't give a very high score.

Acting / Cast: (9.0/10)
All of the cast did a good job. Jongsuk, well, we couldn't expect less from him, he nailed it as usual. Jung Hae In was very good to and so  Suzy. The special characters that were appearing in the drama were very well interpreted by their actors and actresses.

Music: (8.5/10)
I loved the music! I'm so addicted to Suzy's song.

Rewatch Value: (7.5/10)
The drama is good but I think it's because it's interesting and intriguing in the first time you watch. I don't think it would be THAT interesting and cool if you watched it more often, so I gave this score.

Overall: (8.5/10)
The story is interesting, the characters are cool and well played. The drama contains several different characters, each one with their own story, some more interesting than others. He loses a bit of rhythm in the middle of the drama but overall, While You Were Sleeping manages to hold you to the end. I recommend :) :)