The quality of Alyx’s facial animations really drives home that the key is technique and finesse, not technological brute force. The game came out a decade ago and it’s got better facial animation than all of the modern CoD games combined. They built a phoneme engine from the ground up, used it to generate rough lip animations for the game’s spoken dialogue and then hand-tweaked each animation until they were perfect. Then they built a whole expression/gesture engine from the ground up and individually choreographed each scene: not only could Alyx turn to look at the player and roll her eyes, she could do it while blending into any other animation. You can blend running with talking and head-shaking and pointing and limping, if that’s what you want to do. It’s really potent.
They studied human language. They studied the art of animation. I believe they even hired a linguist. The end result is so good it’s practically timeless. And I’m not ragging on CoD games, they look great, but the lip-sync and choreography is still not up to the high water mark of the decade-old trendsetter Half-Life 2.