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. 
Bespoke pixel art is an unbelievable amount of work. I always like the example of Dead Cells where the art guy had too much work to do by hand so he went with low-poly models run through a pixelization filter and exported to a prerendered sprite sheet. Much, much faster than working by hand, and it also allowed him to do things like easily adjust animation timing and minor movements without needing a whole new sprite or a weird visible pause in the sprite animation. It's like the opposite of Donkey Kong Country, which did prerendered sprites for the high amount of detail at the time, he did it because it's so much less work these days.