Honestly, after finishing I was glad I held on. Who says what, for me the first half of the show felt watery and dragged, like where this is going. But around episode 8 to 14 things started to pick up and peaked finally with the main 'WHO did it' plotline. After looking back I admit there were places that looked unnatural or unnecessary, but many things still had their own sense, especially after watching the show completely many things fell into place to me.
Unfortunately, due to the run time of full 16 episodes the storyline may look watered down, but the general direction of it is: introduction stage, the story of Do Ha and Sol Hee, the stage of 'WHO did it' and the story is wrapped up. At least it was framed up nicely at the end.

Characters and acting.
Sol Hee - I'll be honest, at times So Hyun felt unnatural in her role, but at other times the chemistry between the characters picked up, but these are my own impressions of her. While Sol Hee is a pretty straightforward character, to the point of bluntness / rudeness. Understandable, she grew up hearing lies and it was as if no one was sincere, thus her trust for others is null. But her involvement with Do Ha felt like she got enlightened, because he was of very few who never lied. Although it might sound strange that she's so old and can't distinguish which lie serves which purpose, but who was there to guide her? That's right, no one. Even the peaceful times with her ex ended with a break-up as a result of misunderstanding. But I was honestly happy by the ending and how the integration with the neighborhood served her to be more in the crowd unlike her childhood, yet funnily the one she took a step to be friends with is the one she worked with. Thus I wasn't mad at the filler characters of the neighborhood :D
Do Ha - I must applaude Min Hyun, he nailed it to me. Also his character had wider arc, because he went from the stage of being social phobia to slow integration, to finally getting rid of the shackles that bound him and faced the past. I finished the show for his sake. It's not because of redemption, but he was endearingly sweet and nice. Especially in their relationship. Although it felt a bit awkward at first, but later I even found them cute. It was also gratifying to see his character slowly opening up to life. He was riddled with guilt, but exactly this did not allow to see another direction in investigation from the beginning.
Kang Min - I don't understand why some ppl felt against him. He's actually quite good, he only had a moment of anger against Do Ha, but he was almost the only one who did not stop being a good cop. He never used 'murderer', but always used 'suspect' and he also did not give up to find out the truth, while it felt that others believed that Do Ha was the one. At least this makes him good. He truly loved Sol Hee, but not everyone chooses to go through hardships together, I know plenty of ppl who prefer going through it alone. Thus he let Sol Hee go, but in that time her heart no longer belonged to him.
Syaon - excuse me for my French, but initially she was like a selfish, stalking, toxic bitch. I understand that her characters was redeemed, but I just hated her for what she did in ep4. F u, girl. She was basically like a copypaste of Do Ha's ex, but at least she wasn't completely lost. And that was a big difference. But honestly to me sometimes her acting was a bit not up to par. And also that opened mouth reminded me of Stewart so much lol
Deuk Chan - I'll be honest I interpreted his character in different ways, while the story was being told. And you can't help it, because he is so protective :) The actor played really well I think.
Side-characters: Who said something that there are too many? At least the picture did not feel empty and many served their purpose. Sometimes not only the story drives characters to evolve, but also other characters. The neighborhood bunch was shortened down to few people, they served their purpose of two main characters integrating with others. Do Ha's ex played really well, hearing her story makes you feel less negative about her, but she developed into unbearable girlfriend and caused scenes a lot. The brother of Eom Ji also played well. BUT the biggest prize still goes to Jin Kyung, after seeing her stoic image in Attorney Woo it was such a big contrast to watch a mom who is a fraudster, also is afraid of her own daughter and has an awkward relationship, yet I found her really fun.

As for 'WHO did it' plotline. Usually in such stories it can be divided into: exposed culprit (Like The Hannibal TV series); half-exposed (when maybe it doesn't really matter who the culprit is or the movie-makers just want to tease viewers), but we watch them in intermissions showing only body parts (like hands) we don't see the full face; last are fully concealed (when creators don't explicitly show who the culprit is), so you can guess it by yourself.
Because we're watching romance and that means impossible for creators to be this crazy and make the male protag the culprit, meaning it's someone else. And also, it would be a huge flop if they assigned some random dude for the role. So after watching the drama for some time and touching upon the past you realize that it's the third, concealed one. But if you later put 2 and 2 together, you basically have your suspect list narrowed down. But it wasn't without a twist :) Tbh looking back I realize that some scenes have a different meaning now, but it was quite satisfying to see how it happened and more importantly why. Who knew~, who knew~.
At least with this plotline I was satisfied :D

In a conclusion, I was satisfied with the drama, how it played out. It wasn't the greatest beginning for me, but the second part made it better. The actors did a great job, Min Hyun deserves the praise, he made me hold on and actually in the end I was glad I did. And many others deserve compliments too.