Clannad ~After Story~ is much better than the first season. There's the clarity of the plot and how the story goes. As well as the characters. Although it will make you cry or maybe pissed with some of the characters ( well, maybe also for the protagonists ) because it has this "drama" genre. It is the continuation of the first story. This is more romantic than the first one. There are more twist than the previous one ;)
The art is VERY GOOD! The eyes, the hair, the body, everything in it. It is skillfully made. Especially the girl lead and her daughter. I like them a lot. They're so kawaii*.
The sound effects? as far as I can remember it's okay. The Ending and Opening song is not really remarkable, but yeah, it's okay.
The characters are good. The female lead has this compassionate attitude but very unhealthy and because of this something will happen about her. The guy lead is actually strong yet fragile inside. And because of this, they make a perfect couple. They are opposites but really match. the supporters are also important. They color the story and the leads as well.
You'll really enjoy it. But I was kinda disappointed at the ending. I mean it's VERY COMMON -___-
*cute in Japanese