It's Skyrim for me. Growing up I've never played any games (because GiRLs DoN't GaMe) but I've heard some of Jeremy Soul's Skyrim tracks on YouTube and was completely enchanted. Learned that it is from the game, decided to try and now I'm a gamer, lol.
Oh, and also the main theme of Dragon Age: Origins is just divine. And honorary mention to Mass Effect and Witcher music too.
Yeah, I know! I've played Oblivion eventually, too.
It's just that Skyrim OST was what introduced me into gaming and for that reason it has a special place in my heart.