Two weeks into the Winter 2008 season, and I can easily say that Shigofumi is the current "must-watch" show of the season. Two episodes in, and it has already shown itself to be better than any show from the Fall season, including the ones that are still currently airing.
So what makes this show so great? Several things really. First is its concept - letters from beyond the grave. One of the key themes presented early on in Shigofumi is that these are the "purest" of thoughts, the voices left in our hearts when everything else (our life, body, fortune, and existence, according to the anime) has disappeared. Essentially, it speaks of regret, and at the same time, hope, especially with the letter presented in the second episode. It's almost existential in a way - strip away everything, such that only what you really want to say remains. How these letters differ in subject and tone, from person to person, speaks about those individuals' life experiences, and the circumstances leading up to their deaths. In short, it's a very unique way of looking at human interaction, from the cold and plain statement of Asuna's father, to a letter of love and confession from Shouta, to a letter of hope and the future from Asuna, they all speak matter-of-factly about the way those individuals viewed the world.
The potential for tragedy in this anime is very high, and it's not looking like the bland, cliche'd tragic elements so many anime are relying on in this day and age. In Shigofumi, it's very easy to see where things could have gone differently, to where an unspoken word or undone action could have made all the difference in the world. Hopefully the later episodes continue in the trend of the first two, and the writers don't run out of steam, since so far, we have a helluva show on our hands.
So yes, definitely pick this up - a few minor annoyances aside, this can easily be the best show from the season and one of the better shows we'll see in 2008.