Overall :
Yes, it was melodramatic, but what did you expect ? You can't have THAT plot and not include sad scenes. But it wasn't as melodramatic as the other reviews say. I too thought it'd be 20 episodes of "oh no I'm gonna die" but not at all. The plotline is so much more than just the main character having an uncurable illness, and we barely even see the illness's effects during most of the drama.
Besides, it looked genuine (thanks not only to the script but also to Woobin's acting), and I think it's the most important when knowing the difference between a bad melodrama and a good, sad drama.
Both the beginning and the end  were genuine and amazingly done. The middle did look a little messy, but how can you miss out on that drama just because it's "too melodramatic" ? I strongly recommend it, and I think it could suit anyone's taste since it's not just romance or tear-drop-material.

Story :
The first part of the story is satisfying - we don't have to wait to learn about the illness since it's known since the very first scenes. There's nothing in the first episodes that frustrated me. The flashbacks are well done and there's no unnecessary flashback-related cliffhangers but there's still more to learn after every episode. The beginning is really interesting and well paced. I couldn't believe the episodes weren't 20 minutes long.  The fact that they focused on the documentary and on the main characters wwas something I appreciated.
But then comes the second part, and it got a little bit boring, with many, many, many scenes of the Choi family doing their boring stuff. It doesn't help the plot either, it's just like it's a side plot that will eventually come in handy. I skipped some of those scenes to be honest and it never affected my comprehension of the main plotline. Talking about the main plotline - the main character gets hard to understand and relate to. It's frustrating because everything could have been so much easier with just a little communication but no !! He has to do dumb stuff !! Anyway, during the middle part, we barely even hear about the illness and the documentary (which were the plotlines I craved for). It transforms into a thriller. I liked it, but I probably won't remember half of what happened in those side-plots in a week.
And then, the final part.. cleared up all the built up frustration of the middle part. No more useless scenes, back to talking about the documentary a little bit, back to talking about the illness and actually being ill. I finally could get attached to some of the side characters. I cried a lot tbh.
Overall, I'd say that the story gets a little... distracted ??? in the middle, but it helps to show how determined the main character is to clean up his mess before leaving. It is frustrating, and the relationship between the two main characters is a little weird, somehow obsessive, but interesting. I liked it. I also like that we knew how it was going to end, from start to finish, it was clear, and helped guide us through the more prone-to-confusion side-plotlines

Cast :
Suzy was okay, the actress who played Joonyoung's mom was great and overall most of the characters related to No Eul and Joon Young were good actors, But!! There are two actors I really didn't appreciate : im joo hwan (choi ji tae) and Im ju Eun (Yoon Jung Eun). Choi Jitae was hard to play since he's already a blank character, but I really didn't feel like he suited the role at all.
I'm still giving a great note because Kim Woobin's acting was amazing. His sleeping face is more expressive than the whole Choi family (except Haru). He's a great actor, what more can I say.

Music :
The songs weren't outstanding but the ambiant sounds were great at building up tension subtly. It wasn't too "in-your-face" but I feel like they did a great job on the sounds, more than on the songs (not saying the songs weren't good - they were - but I think I'll mostly remember the small ambiant details rather than the main OSTs)