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. 
I used to be crazy about open world levels but eventually my need to experience it all made me hesitant to play as who's got the time for that? I eventually resolved myself to finish as many of my linear games as possible and realized actually I very much like my linear games.
i've also experienced that, but upon actually doing all the various activities in some open world games, i realized they're often just filler bullshit or boring little minigames. like its almost always "hey here's my shooting competition, go to different points of the map to shoot targets with a timer". its just lazy.
Yeah, you can really feel when the amount of gameplay hours isn’t proportionate to the amount of design time that went into padding them out. I think unfortunately from the devs’ perspective it feels proportionate because the systems to dynamically generate new tasks themselves take time to develop. But there’s only so much variation that can be produced while keeping the results predictable (read: fun and not broken)