What's the anime Clannad like?

I've heard some rave reviews about Clannad but also some warnings that it's extremely sad. Many people have said it's so tear-jerking and anyone who didn't feel anything is a souless monster and even the critics said that cynical souls will avoid shedding tears. Is it worth watching or is it another one of those overhyped, worthless animes?? I've seen some animes that are raved and aren't worth it so don't flame me for that! I haven't seen it yet.