The most helpful review does cast some doubt on the quality and story of the anime but I do not agree with that (hey, it's a review, subjectivity is synonymous with it).
I think the characters were well developed. Some lapses in the story and plot with the letters and the reasoning of the whole "time-capsule" but then again it's not the main focus of the anime (like Steins Gate which is all about this sort of stuff). The sound was really good and the voicing was even better, really emotional.
However, there are some bigger downsides to this anime that I must admit do make the experience less fullfilling. It is a bit too melodramatic at times and needs a special mood to watch this. Perhaps it's the situation I'm in (just moved to university and it's been really tough being alone and in an unknown environment) that made me connect with the sad aspects of the story as it helped me release my own anxiety.
To me, this is a great anime that is worth watching. It's not long and by no means unwatchable because of the overly dramatic parts. It does need a specific mood to make the experience enjoyable. So if you're expecting some happy slice of life anime, this isn't it; at least I don't think that's how it was meant to be perceived.
I would recommend this.
