Not sure about skin rendering, but way back when Half Life 2 was new, one of the ways it pushed things forward was with the facial rigs and animations.

At least as far as I remember from gaming news at the time.

I remember reading that it was a big leap in terms of matching real facial muscles to the 3D rig face “muscles”, and in using those little dot things to capture actual facial movement of some of the line reads. I think Valve’s discovery and/or usage of the fact that real eye iris angles are offset by about 2 degrees was also something that was noted as a big move forward past the uncanny valley.