I have two solid examples, both of which have been, to an extent, robbed by time. As a kid, I really loved the ending to His Dark Materials (the book series of Northern Lights/Golden Compass, The Subtle Knife, and The Amber Spyglass), precisely because the note that it ended on was bittersweet and left me feeling very tender about the whole thing.
The other is (surprise!) the ending to the original Dark Souls. While it is, on its face, a fairly unimpressive ending (particularly in the base game), repeated plays (and exploration of the alternate paths) really gives both of the endings, and the world, a layer of poignancy. The addition of the DLC only further complicated the picture, but made continuing to think about and explore the conceptual space of the game better. I really loved the ending. And then they made two sequels which undo any finality to it. Ehhh.