I Played through portal again to get myself in the mindset. I wanted to have a mind full of Weighted storage cubes before I started looking at the theory of study. One thing I noticed from a theatrical point of view, There is very little music. There is the occasional radio in a Rat Man nest or with a few cubes. Other than that, I can think of only really think of a few moments with music. The moment when you finally get the full Portal gun, where you can fire two portals. The music is bright and and technological. You were just given the key to a new world, and the quick musical moment adds to that feeling.
Another is when GLaDos tries to incinerate you. The music is sharp and dreadful, kind of like a techno Snidely Whiplash moment.
The final moment I really noticed the music was during the climatic battle after you burn away her Moralty core. It is your standard climactic moment music.
Now this serves two purposes. The first is the lack of music. This gives the environments already sterile and solitary feel even more alienation. The second, in my opinion, is to give GLaDos a flare for the dramatic.