This is a beautiful fairy tale-esque drama and I was surprised to see a western religious philosophy being used. Honestly, I came in with low expectations but came out a believer.
The main leads have great chemistry on screen and portray their characters wonderfully. Both Shin Hye Sun and Kim Myung Soo did well in portraying the innocence behind their characters while still maintaining their central personalities. Even when the characters fall to their lowest points of desperation they remain believable and empathetic (and very human, despite the fairy tale setting.)
There are repeated themes you see in other asian dramas (such as a past connection, a rich main lead, etc.) but plenty of unique themes or underused themes that, when mixed together, create a memorable experience for the viewer.
I felt the story flowed logically from one scene to the next. There was plenty of comedy sprinkled throughout to keep the atmosphere light for most of the show and enough fluff to keep romantics satisfied even from early on. The ending had enough closure for me but I would have been happy to have just a little bit more. :)