Clannad is good, but suffers from being Pure, Undiluted Key. Like, after Kanon, which was good, but in part trainwreck (WAY TOO YOUNG CHARACTERS!!!) it's hard to take a show/vn with the same concepts at face value and expect an equal reaction.
Had Kanon never been, and Clannad landed at some 35-40 episodes, fully fleshing out several of the butchered arcs, with a fulfilling end of choice, then shit would have been Awesome.
I have watched AIR over eleven times now, and it's still just as good. AIR is quite possibly one of my favourite shows, EVER.