My main problem with Clannad After Story is the first 8 episodes; those episodes really serve no purpose then to develope side characters from Clannad who don't really need developing. I just wanted to see Tomoyo and Nagsias' relationship develop - however after episode 8 this soely becomes the focus of the series - the ups and downs of there relationship and Tomoyo really develops into one animes best characters. Episodes 16-22 have some of the saddest moments I have ever seen from an anime and will test those with hearts of stone (I sobbed about 3 times during those episodes - episode 18 was the saddest).
Clannad had far more of a focused story then After Story did, but the later half starts to become far surperior simply because of how emotionally engaging it is - if it wasn't for those first 8 episodes then Clannad After Story could of been a masterpiece.
BBFC rating - 12 for moderate violence, language and sex references