Some games have some really great soundtracks. Some songs are memorable, nostalgic, tense, sad, and so on. I personally love the Silent Hill 2 theme, the Metal Gear Solid 4 theme, but I think my all time favorite video game song has to be Gerudo Valley's theme from Ocarina of Time. What about you?
EDIT: I'd also like to add the Halo theme and Demon's Souls. Love it or hate it Halo's opening theme kicks ass. As for Demon's Souls the intro cinematic gives me chills every time I watch it. When that woman's voice comes in it's just crazy.
EDIT: I'd also like to add the Halo theme and Demon's Souls. Love it or hate it Halo's opening theme kicks ass. As for Demon's Souls the intro cinematic gives me chills every time I watch it. When that woman's voice comes in it's just crazy.