I'm not sure how much this song hits with those who haven't played the video game Portal, as the lyrics (written by Coulton) directly reference two different video games in heavy detail. Certainly, the game version sung by Ellen McClain has more appeal within game. There's also a live version sung by Felicity Day that is entertaining, but with poor quality.
This particular version of the song with Sara Quin singing and some beautiful use of the theremin is my favorite version. Even if video game music isn't your thing and the lyrics don't make any sense, this is just damn pleasant.