1. Ocarina of Time - My favourite ever attract mode music. The peaceful footage of Link riding Epona across Hyrule is a big part of it, but it's those opening chords: https://youtu.be/CtMllWsML5M
2. Battle Garegga - Fly to the Leaden Sky. I could have easily picked one of many soundtracks Manabu Namiki did for various Cave games but this is the one which most gets me instantly into the mood of the game, it feels like the start of something special. It keeps moving up through the gears but never gets too intense, it's energetic and warm and shiny and euphoric, but with a little bittersweet tension hinting at what's to come: https://youtu.be/UF-ENkufyCY
3. Robocop (Gameboy) - Almost a cliché at this point, but it's still astonishing to me how much depth of feeling there is to these chords and the buzzy flute synth lines winding through the track. It's got that same Garegga quality of sounding euphoric but also slightly sombre: https://youtu.be/wGIKnn-COS4
4. Demon's Souls - Souls of Mist (Character Creation theme). This was my introduction to the Souls series and it instantly got under my skin. It perfectly describes the mysterious, beautiful, fragmented, decaying world of Boletaria, and its timeless echoes of the past: https://youtu.be/s3nckWeT-m0
5. Final Fantasy VII - Main Theme. One of the most important pieces of music to me, this still stirs so many emotions more than half a lifetime after first hearing it. It's brooding, gentle, anxious, triumphant, mysterious, yearning and glorious. It instantly transports me back to the wondrous feeling of stepping out onto the world map and having my mind blown by the realisation and anticipation of what FFVII really was. I'd never played anything like it nor heard anything like this in a game: https://youtu.be/6UARM4q7hHU
6. Super Mario Galaxy - File Select. I know it seems obtuse to burn my Galaxy choice on the file select menu music, but like Demon's Souls, this sets the tone perfectly for what follows. Despite the joyful, mind-bending movement and level design, at its heart Galaxy makes me feel peaceful and lonely. The observatory music and various galaxy hub themes have a similar atmosphere, but this is the simplest, purest and most direct in how it expresses the core of emotion of the game: https://youtu.be/HwWWW_kAeAc
I'll come back and fill this in by rows. Great thread!