I disagree with your Human Revolution pick OP, because it's a big demonstration in my mind of the divide between a melodic and ambient approach to game soundtracks. Aside from parts of Icarus, there's really no track that springs to mind when I think of the Eidos-Monstreal Deus Ex games, whereas I've had just about every track in the original game stuck in my head at one point or another.
For example, going into Hengsha in Human Revolution you've got this:
Heavy on ambience, but not something that sticks in my mind. In one ear, out the other by the time it's over. Contrast to entering Hong Kong and hearing this in the original: