Mostly about effectivity vs. efficiency in terms of game programming.
Portal 2 Soundtrack
I haven't played Portal 2 (just watched a Let's Play) and almost failed finishing Portal 1 - I didn't manage to beat the bonus maps. However, what always fascinated me was the music and I was even more fascinated as I listened to the full Portal 2 soundtrack. It has the awesomeness level like Half-Life 2 and even boost with a few chiptune-esque elements. It's so damn unique, I can't repeat how highly I recommend it. Just get it from somewhere, it's worth your precious attention.