Great atmosphere, interesting lore/backstory, good world building, heavenly/melacholy OST, fun times, sad times, more sad times, philosophical talks , finally…bittersweet but still sad ending.
That is all I can describe "Shoujo Shuumatsu Ryokou". And now look at its popularity/amount of people talk about it:

But seeing it here combine with my favourite Japanese meme:

Still dying for adaptation of the finale.

I laughed when I saw Nuko being used as the microphone