It's a tie between the conversation with Vigil in the original Mass Effect and the final confrontation with Dagoth Ur in Morrowind.
"Remembering the melancholy of human existenceMikailCaboose said:Surviving Touhou 7: Perfect Cherry Blossom on Lunatic. Got to the final spell card (a damned time-out card no less) for Yuyuko with no lives and one bomb left. That theme never pumped me up like it did then.