Solid but not spectacular. If you like time travel dramas I would give it a go.

The good:
The story is interesting and keeps you entertained. This probably the strongest aspect of this series. The short running time of each episode moves the plot along quickly. I liked how we got to see the link between past and present timelines play out.
Standout cast for me were Yeri a Ha Rin and Kim Yi Seo as Hye Min.
The friendship between the leads is very sweet and adds so much needed comedy at times.

The bad:
It's definitely from a smaller studio, evident from the OST, script and acting. This is not a direct criticism per-say but worth bearing in mind if your viewing time is limited! I didn't find the OST memorable, some of the dialogue is pretty basic and there's a few crocodile tears. Also you get the feeling with a bigger budget they could have done a lot more.
The kiss between the two leads was a very poor effort.