The epic chants/shouts are awesome. Goosebumps.
Haven't really noticed music outside of that. My fave OST is still probably ME1. It was just so unique and fit the mood of the game perfectly.
"That's the reason my FFL team name is TrentGreenLeadBlock. When you see this mother****er coming around the corner on a block, put your children to bed and batten down the hatch on your girl's snatch, because the same power that destroys defenders can scar the minds of the youth and simultaneously impregnate any woman within sight, live or on television."