I think it should be a rite of passage that everyone experiences the heart-wrenching pain of watching Clannad and Clannad Afterstory. It doesn't get much more beautiful than that. Similarly, Anohana is emotional torture in the best sort of way.
Also, if they ever remake Angel Beats but give it more than 12 episodes to progress and develop, I think it would be absolutely amazing. Also if they fix the glaring plot hole at the end. As it is, Angel Beats still has just about the greatest soundtrack in the history of anime and the premise is still amazing. Just too much content jammed into too little of a time frame.