It’s a good show, definitely worth watching. The animation is amazing, and there are some really good episodes. I was kind of let down because I was super hyped about it when I started watching and it didn’t live up to the hype, but it still a good anime.
It's a poignant drama with a post-war setting, and about how much a letter can mean to both, the writer and the receiver.
I agree with @Bigfrost2 in that the animation and story are really great. I loved both, the anime and the light novels. The anime differ quite a bit from the light novels; if you want to try both, I'd advise watching the anime first.