I must say that the best part was the great voice acting of the characters, there was a great chemistry between them. Also, the writing was crisp and kept everything moving.
Most of all the general theme of tragedy is what made it great. From the first episode I saw in the season 1 which was the last episode of that season, I knew it was something good, because it got an emotional response over a character I was only introduced to in that episode since it was my first. I got so misty eyed at the burial scene I knew it was something good. Something about tragedy makes something fantastic.