It's also worth noting that Valve optimized the Source engine even more with Portal 2. Upon starting up the game, EVERY video setting was maxed out, and ran above 40 FPS the entire time.
I could never do that with Half-Life 2. The recommended settings were always lower, and if I tried to max everything, my FPS lagged behind. I'm astounded that Valve managed to make an engine this robust - 6 years later, they continue to improve it and it shows no signs of being "outdated".