Beyond Goodbye left me with an immersive feelings. Sad but longingly beautiful. If you watched this series because Kentaro's latest kdrama What Comes After Love and not a fan of sad ending, sorry to say but this series is just not for you because this is jdrama where the illness/sad troupes are pretty common. However, for me who used to this kind of ending in jdrama found the ending pretty satisfying. Keep in mind, the main focus of this drama is not romance. This drama deals with grief, loneliness, memories, longing, sacrifice and etc.

The cinematography is amazing within 3 different countries (the sea, the mountains, the coffee fields, the apple farm, the railway track) and the four seasons are shown plus with the storm, they are such breathtaking sceneries, the great and natural acting, the subtle moments, the emotions, well written scripts, marvellous casts, beautiful osts and of course the best ending song by Kenshi Yonezu.

Each of the character is so passionate, deep, complex and empathic especially the five main casts. I personally like Saeko's personality. She is ambitious, fashionable, optimistic, fun, independent yet buried her burden, deep inside her heart and only visible to others closest to her.
I can relate to Kazumasa's confusion with the heart beats for other woman other than his wife, who he loves so much. Even I as a viewer got confuse with the mixed feelings he has. He is kind, sympathetic, a very good man.
We all feel bad for Miki, a wife who trying to protect her marriage as she should. Watching her husband slowly becoming a different person, loving a thing that once strongly disliking can be devastating. She is an honest, patience and caring person.
The best character for me is Yusuke. I know, there is not much of his scene but from others' POV, we know he is a good person, goofy, simple yet deep (fireworks is the best, right?).
And lastly, Kengo, an emotional best friend, a good listener, readily to give an advice, so that none of them were hurt.

I will recommend this series to whoever like to watch from different kinds of perspective, not just from one character but all of them and understand why the characters make the decision that way. They all have flaws and make mistakes like all human do, something you can relate too.

Major spoiler after rewatch.

Hurm..I know a lot of people turned off by this series mainly because Kazumasa was indeed a married man. Is he cheating on his wife? Yes, clearly he was. Then, is this series glorified cheating? Of course not. Even he isn't married, he will also be cheating if he has a girlfriend. This is because the series intended him to has a wife.

Even if Yusuke's heart function healthily in Kazumasa's body, the series will be finish on episode 7. Kazumasa already made his decision to stay with Miki because he remembered the promise he made. To be a goofy husband and wife so that he feel that he is really healthy and alive (after he saw a sweet banter between Saeko and Yusuke). Besides, he promised maybe they could have kids in the future (clearly, they couldn't before this) and those had to be broken again. Also, he didn't wear off the ring until the end.

And Saeko's made a decision not to meet Kazumasa again even though she loves him because she knew the boundary and reality of the relationship. Yes, we all hate the kissing scene but what led to that scene? Because there wasn't technically an affair between them (according to Miki), thus, having one is easier isn't it? Saeko was the one leading Kazumasa but gradually stopped herself. Then, she remembered Yusuke and reminisced herself with the memory of her and Yusuke under the umbrella which leading to the decision she made that I stated earlier. Lastly, Saeko put off the necklace with her engagement ring in order to move on and forget the tragic accident and kept the boots and umbrella instead that I believe contained both memories of Yusuke and Kazumasa altogether.

Then, we got served by episode 8 as the proper goodbye between Saeko, Kazumasa and Yusuke that I believed a significant and satisfying ending. Maybe, part of Kazumasa wanted to see Saeko but he also wanted to be fair that Yusuke's heart was dying inside his body. Last message to Saeko from Yusuke was smile and be happy which Kazumasa sincerely conveyed as they exchanged the handshakes and hugged as their last goodbye.

Again, these will be my interpretations. Do not expect the chemistry because romance isn't really a focus of this series. This is not kdrama. No chemistry chemistrying here. (Even the piggyback scene felt sad). And I didn't really know why people said the romance was forced. Maybe because Kazumasa is a married man, that's why he restrained himself?
Please, make another drama between them where they can end up together (this is their forth drama where they got sad ending..haha)