It’s a very good drama. Not nice, nothing is nice in this one. I've been watching j-dramas and k-dramas for almost two years, and without a doubt, this one is the hardest I've ever seen. So, at I said before, it's good but you should be ready to cry a lot from beginning to end.
Acting: Miura Haruma is simply amazing in this drama. Nobody could have done this lead better than him. The rest of the cast was ok too.
Music: I liked it. Most of the time it was right for the moment… And it made you cry even more.
Rewatch: sorry, but no. Although the positive and meaningful moral of it, I didn't like the end, and it would be too difficult to see it again.
So, if you are a hard crier, cold-hearted, and/or you are not afraid of watching a really good sad drama, go for it. It's worth the time.