Used to be symphonic or gothic metal, but the older I get, I'm starting to prefer silence or white noise like rain or whale song, hahaha, easier on the head.
Slow jazz is pretty decent too, like the ones you see in those old timey film noir movies.
Some games have a carefully curated soundtrack that really helps elevate the experience, but a good chunk of the time its the same handful of stock public domain songs you've heard in a thousand other games. In that case I just play whatever I'd normally be listening to instead anyway.