I am a big fan of the animations of "Key".
I watched several animes made by them and liked it (esp. Kanon, Clannad & Air)
Honestly, I believe that Key can create wonderful characters and animations but there is always something missing in their stories.
Air is one of the anime that I found very interesting but the ending wasn't what I really expected. I thought that it would be a wonderful climax but it let me down. Nevertheless, I still find this anime (and all anime made by Key) amazing and touching.