I play most of my games with background music (usually turning off music in-game, as it is very rarely anything
I want to listen to for hours and hours). It's amazing, really, how sometimes a new song starts just as you're opening
a door to a dungeon. I have a long playlist on shuffle. It's a mix of abstract/minimalist electronic and experimental music:
Tod Dockstader, Eliane Radigue, La Monte Young, Infinite Frequencies, Brood Ma, Phill Niblock, Alvin Lucier, Pauline Oliveros. I add
in some recent rap/pop music, such as Lil Wayne, Tinashe, Bladee, Milo Mills. Instrumental dance music mixtapes are great too
(deep/tech house). And then some classical music too, like Brahms' sonatas & concertos, maybe some piano music from Satie or Chopin,
you know, basic classical stuff. Pretty much everything works great, but I tend not to have music with lyrics, save for the one or two
current fave track.
Best experiences have been playing Shadowrun: Dragonfall with that stuff on (the combination of dance music & abstract-y drones
works wonders), and then listening to a lot of Black Metal and Noise while playing Half-Life 2.
I actually really like Avadon's in-game sound effects and ambiences.