Ah, wow. This truly was an amazing anime. I doubt I could find any little thing to complain about while watching it... Except for one thing. It kept me awake watching episode after episode, and I ended up failing a math test due to lack of sleep. But, hey, that's just a testament to how great this series is.
Anyway, I'll start with the characters and their personalities.
I personally loved every single character in the anime. From the minor Daiikuji-chan to the four main characters, I enjoyed watching every one of them. Especially when combined with the absolutely beautiful and heartwarming storyline, the characters were absolutely wonderful, in almost every way.
The storyline, however, is where this anime really shines. I found myself crying for at least 3 hours, in a row. It was so amazingly dramatic and sad, yet, at the end, let everything turn out acceptably. So many scenes caused me to cry, which is a great thing. ^_^ Truly wonderful.
The opening song, is a little upbeat, but not to an extreme extent, and, although is a bit contrasting to most of the storyline, is very nice. However, the ending, and the final episode ending perfectly captured the essence of the anime with it's slow, peaceful, yet somewhat sad sounding tune. All the background music fit perfectly, further bringing out the soul and feeling of the already-dramatic storyline.
All in all, this anime was amazing in all ways... Watch it!