Also the scripted sequences that were all in-engine were amazing at the time.

We were used to cool things happening in a pre-rendered cut scene before, but with HL1 everything happens from the player's perspective in real-time while you're in control of them. Even the opening where you put the crystal in the beam and actually cause shit to go haywire felt like an incredible moment of player agency in the world. Like oh man what did I doooo

EDIT: oh @massive_bereavement@kbin.social kind of beat me to this point haha