Mass Effect 1, the final bit of the end
Spoiler where they're digging the team out of the wreckage of the council chambers, all sad that Shep didn't make it, and then Shep comes climbing out of the ruins
Very stirring, even on multiple replays - good combination of music, scene-setting, etc.
Mass Effect 3, the various plot-resolution story arcs for several of the party members & their factions. Like Mordin. And the Quarian-Geth conflict... especially the "bad" ending. AAAA! So sad when
Tear up just writing it here.

So glad I managed to avoid that in-game, and only saw it on Youtube.