The question has to be broken down in subparts: Background music. Normal sound effects. Lewd sound effects (including moans and gasps). Actual voice acting.
Of course these can be subdivided further and also overlapping. For instance some games have background music that we the player hear but which is not happening in the game world, and also music that
is happening in the game world like if a NPC plays an instrument. And a game that is voice acted might also have the voice actor do lewd noices including words spoken in lewd scenes.
The games that have music so good that I leave it on are so few that I can probably mention them from memory directly.
Lessons in Love is the prime example, where I actually tracked down a lot of the music and put in my mp3-player. Best example from LiL is probably
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, pretty much Anime perfection.
Tales from the Unending Void is another one where the music really works. Where LiL's best music imho is about damaged vulnerability, TFtUV's music is all about the space and sci-fi feeling, and as all sci-fi buffs (and obviously Perverteer) know scifi is all about Sense of Wonder, which the music conveys perfectly.
One thing that I realize now that I think about it is that I generally want background music to not have any lyrics, or if it has that they are in a language that I don't understand at all.
I generally like a bit of lewd sound effects, unless they are over-the-top or obnoxious, and also they can't be reused too much in different scenes. It can be a bit problematic if the characters are hebe or loli, but have a bit too adult voices, and I have to mention
Rational Chaos as a game that at times fails a little here. (yeah I know all are 18

) I still keep the sound effects on in RC, but some of the girls sound a little too adult. ( i do love the game still, Goose)
Actual voice acting is not so common in he first place, and often not so good. The games that does nail this is
Ravager and
Passion Project.