I had never seen 火垂るの墓 (Grave of the Fireflies) before today, and it's brilliant, extremely sad but more than anything incredibly powerful. Even with the very first sentence, spoken by Seita, being 「昭和20年9月21日夜僕は死んだ」 ("On the night of September 21, 1945, I died" ) and so trying to prepare viewers for what is to come, I still wasn't quite prepared.
If you haven seen it (but most of you probably have), please do.