This mainly applies to R18 games, but I can never take it seriously when they use those rock/grunge tracks on h-scenes. I swear it's always so loud too, so I have to pause to lower the music volume.
A favourite of mine, though, is Sympathy Kiss—despite not thinking the game itself was amazing—because the music made me feel like I was in a drama. AIKOTOBA and BYE MY LIFE / FOUND MY LOVE are songs I constantly listen to, and it was always fun to hear them in the story.