Penguindrum. Not the ending itself, but by the time credits rolled in I was still wondering about things like "why mecha bear specifically", "where did Sanetoshi came from", or "is Yuri actually a man, or her lover was referring to the scars", among others, thus diminishing emotional payoff.
Probably warrants rewatching, but since I don't do that... stupefied. Great music tho.
And Makoto Shinkai makes best uplifting endings.