I'll start by saying that if you want a slow-paced drama, this is one that has a lot going for it. My overall impressions -
OST - exquisite. The music is perfect, blending the beauty of classical piano with the sadness of a cello, and some beautiful songs that flow effortlessly throughout the show. The music was excellent at pulling emotion out when the script itself wasn't able to accomplish it.
Cinematography - I think this is the most beautifully filmed K-drama that I've seen. The camera filters that give so many scenes the filmy/artsy look. The play of light and shadow was brilliant. Some very good slow motion work, and I loved how most of the show was dressed up in pastels, nothing bright and jarring, save an occasional pop from a red sweater. Him walking through the woods near his childhood home was gorgeous, and the snow scenes were amazing. So, actually, I'd have to say that most of my love for this show vacillated between the OST and the cinematography. In my mind, while I was watching, I kept saying, "pretty!"
Costuming - nothing too attention-getting here, but I had to mention the trench coat that Jung Hae In wore in ep 11 with the leather collar and accents. It was just beautiful and it conveyed power and anger in the scene that he was doing at that time.
Acting - excellent. Jung Hae In as Ha Won was very understated and had wounds from his past, though I didn't really feel sorry for him because of the reasoning (to be discussed in storyline). Chae Soo Bin as Seo Woo - she is really lovely. She has those sad eyes but a perkiness about her that is so endearing. She ran a lot in this show, and it was so cute, her running down the alleyways from place to place. The rest of the cast was very good - I loved Lee Jung Eun as Min-Jung, the grieving mother.
Chemistry - the main couple was cute together, but no off the chart chemistry. This was a "comfortable" relationship (kind of like an old pair of shoes), they spent time together, supporting one another and learning more about one another, but I didn't feel any progression of their relationship. There was one kiss.
Storyline - Overall, this was a story of healing. Healing from loss, healing from loneliness, healing from aspirations unachieved, and healing from secrets coming out too late. Each person in the story dealt with their losses in a different way, and I really liked how the writers delved into ways of healing - opening up to friendships, being brave to put yourself out there to someone you like, turning loose of old hurts. I especially loved the scenes in the boarding house, where the boarders would sit on the floor in the kitchen and drink and talk and laugh. They were each getting something special from this bonding. Again, Lee Jung Eun was wonderful as a mom that feels guilt and despair and has closed herself off from emotional contacts. Watching her open up was a treat.
SPOILERS BELOW:
Writing - here's where my problem came in. First, I'm sure others have mentioned it, but the fact that this show was shortened from 16 to 12 episodes because of low ratings is telling. There was a subtle shift in the pacing of the last couple of episodes as they tried to tie up all loose ends. Ha Won and his 10-year unrequited love for someone that went and married someone else was just pathetic (and why did she, anyway?). A lot of the scenes between Ha won and Seo Woo didn't ring true, because he'd been in love with an ideal for a decade, and then after a few conversations with Seo Woo he's moved on? Plus, I felt that Seo Woo was kind of a doormat. I know she was supposed to be understanding of his dilemma, but really, anyone in real life would say "snap out of it!" And the AI aspect was not believable and just kind of creepy. The ending was very abrupt and unsatisfying.