EDIT: Seems dynamic music is back in style in some very recent games, many of which I haven't really played yet. Good. 
For me, it's dynamic music, the kind that some games had that adjusted moment by moment to what was happening in the game.
The best-known example of this in the 90s game TIE Fighter, where the moment more enemy (or allied) ships showed up the music would have a little additional flourish to acknowledge the shift in battle. There were pre-battle tension tracks, battle music, complications of battle, grandiose flourishes for the arrival of enemy or even allied capital ships, and victory and failure music all ready to flow into the next seconds of the game.
A lesser-known but still excellent example of this was in Ultima Underworld and its sequel, where drawing a weapon had its own special "preparing for battle" tension music, getting attacked had a jump-out-of-your-skin joltingly sudden musical start that actually scared me as a kid when I got ambushed, music for battles going well, going poorly, victory and defeat.
I wish more games did those sort of second by second musical changes, but they've sort of fallen out of fashion for the most part. 
You would love Lucio from Overwatch. His entire kit is built around dynamic music and how you're playing the game at any given moment. He acts as the center of a large aura that either gives a passive speed increase or a passive healing stream. You can cross fade between the two tracks whenever you want with no limitation giving you a choice later on whether to amplify one or the other. You can even cross fade while you're amplifying.
The character's ultimate is just a bass drop that animation locks you into slamming the ground. I didn't even mention that you're a sci-fi roller blading support that can wall ride around the map. You can bass drop off the walls or just whatever high place you can. Nobody gets mad at you for looking cool as fuck.
The music is sick definitely take a listen!
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