Mine is Skyrim.
I always come back to its music. It’s uplifting, telling me that everything’s gonna be alright. I have its songs in many different playlists.
Absolute favourite game soundtrack? Frostpunk’s OST. The soundtrack really brings home the desperation and harshness of survival in the cold. When the storm is coming and the music swells up… goosebumps. Every single time.
Divinity 2: Original Sin has a great soundtrack too. Kinda surprised I couldn’t find it in the comments. Minecraft as well. It’s very soothing and calming.
Aside from that, some smaller titles with great music: GRIS, What Remains of Edith Finch, and FAR: Lone Sails.