I really enjoyed Clannad and After Story, but they did the same thing a lot of anime do these days and that's flip you after the first few episodes. No spoilers here, but it starts out as a H.S. situation comedy and by the end of the series you are bawling your eyes out after a few WTF moments. The character development was outstanding as was the animation and the music only added to the emotion.
The only caveat I had about the show was that the creator couldn't let go of the characters. You would see an episode arc and then the series ended, like 4 times. "Let's see what would have happened if this occured, now let's see if this person was with that person". I understand that it's tough to let go of characters you love, "SPIKE!!!!", but sometimes you have to know when to let go or at least create a different series with the same characters, like My-Zime. This show is a definite watch and purchase, just be prepared to be humming The Big Dango Family tune for the next 3 months.