Well Air has an anime-adaption... and I liked it.
The first half is basically your Kanon-fare. Afterwards you have the summer-arc which more or less introduces the real storyline starting way back in the past and after that comes the last arc which basically should be the reason, why people probably consider Air as really sad.
However, I loved it, at least everything about Misuzu and her story including the ending.
The ending is however not for everyone. Can't say more about it.
