Battlestar Galactica, "Revelations"
The entire run of this philosophical space saga was about a ragtag tribe of humans looking for the lost Planet Earth. So you might have guessed two things: that they would not find Earth until the last episode of the series, and however they managed to do it, the reveal would inevitably be a letdown. You would be wrong, twice. In this mid-season finale, the crew of the Galactica finds mankind's ancestral planet after a war that nearly exterminated them, leading to giddy celebration — until they land, and, in an astonishing, wordless closing scene, find the planet to be an irradiated ruin. This sucker-punch of a twist set up two questions for the final run of the series starting in January: Where do they go from here? And where did we go?
(Sci Fi)