Mostly from ME1 and ME2:
Most of this is just 4 notes played over and over again, yet it's so well done, portraying the scene, sadness and triumph perfectly.
to quote from the top youtube comment on the video:
"Every once in a while, there's a rare magic moment in game when soundtrack, game play, and story align in sync and make for a moment of unforgettable immersion. Running through gunfire on Virmire to this track was one of those rare moments for me." This.
both of those are missing from the OST for some bizarre reason. See the above video, It's the same feeling, but not to the scale virmire did it. Those 2 songs still makes adrenaline go through me as I play.
Everything from Lair of the Shadow Broker DLC was awesome, but this song I feel was the best. It suited the pacing and the scene so perfectly.
Because, chanting isn't done enough and well enough in games.