Obviously there are good and bad things to say about this drama as with many others.

One of the good things was the production. It looks well made. The scenes are beautiful. The sets are beautiful. It's a very pretty looking drama.

Another good thing was the cast. With the exception of Lee Min Ho, I think everyone did an amazing job.

The thing that attracted me was of course the premise. I think that was very interesting.

The bad thing is it's very inconsistent and doesn't seem to follow its own logic. The drama is very slow for the first 11 episodes. Things finally start to pick up and get interesting in episode 12, but then starting from episode 14 plot holes start to pile up. Many seem to feel that the plot is complicated, but it's not. It's just full of plot holes, that's all. It's fairly easy to follow, but if you want to enjoy it, I'd advise not to think too much or you'll just get mad at plot holes that could have easily been taken care of. I think most dramas that involve parallel universes or time travel ultimately encounter this problem where they start creating plot holes, because the drama doesn't follow its own rules.

Another bad thing, and that's just my opinion was the casting of Lee Min Ho. He can't carry this type of drama. He looks the part, but misses the charisma to pull off this role. His acting is very boring too. Again, this is a personal opinion, I'm sure there will be people who enjoyed his performance.

Another thing that bothered me were the obvious product placements. I would be fine if they just showed the products in the background or something, but they just went too far in this drama by pretty much shooting commercials for multiple products. It looked embarrassing and uncomfortable for the actors and totally took me out of the story.

All in all, I enjoyed it. I would have liked it to be a bit more fast paced, but it's definitely worth a watch, albeit only once.