I was discussing this with a few friends today - I've always had a soft spot for music in video games. There's something about excellent compositions that invoke insanely strong feelings within me that can turn even a mediocre game into a spectacle, and can turn good games into masterpieces. My favourite piece of music from any video game is "You're Not Alone" from Final Fantasy IX, even 14 years later that music still gives me the most wonderful nerd chills.
I finished Halo 4 for the first time yesterday, and whilst the game itself wasn't bad, I found myself almost in tears during the final section of the last level because the music felt absolutely perfect. The scenery was so good, but the composition while you're reaching the end was the most breathtaking part of that game for me.