Portal OST is like the definition of ambience. You don't notice it the whole game and after listening to the soundtrack you realized how funky it actually is.
I can definitely see the change of pace with both soundtracks. Portal 1 had this clinical and uneasy ambience that makes the player feel utterly alone It definitely matches with what was going on in the lore with the Black Mesa incident happening simultaneously and what was to come in Half-Life 2. Portal 2 changes absolutely everything with replacing the fear of being alone to the fear of getting smashed by a big mashy spike plate.
"Just a heads-up: That coffee we gave you earlier had fluorescent calcium in it so we can track the neuronal activity in your brain. There's a slight chance the calcium could harden and vitrify your frontal lobe. Anyway, don't stress yourself thinking about it. I'm serious. Visualizing the scenario while under stress actually triggers the reaction."
I feel like the original Portal gives off a more 'alone' and 'dead' feeling to it. While Portal 2 gives off a more 'robotic' and 'high-tech' feel to it.
I love how the only acceptable way to describe Triple Laser Phase is with the Triple Laser test chamber itself. I think there's something wrong with it though.